CREATE TABLE little_girls (
  grade FLOAT, height SMALLINT, birth DATE, fatness BLOB,
  hair SET('blond','black'), previous_school VARCHAR(64),
  is_made_of_sugar_and_spice_and_everything_nice BOOL,
  reason_for_existence TEXT DEFAULT 'thank heaven');

CREATE TABLE n (s1 INT, s2 INT);

INSERT INTO n (

INSTALL PLUGIN plugin_name SONAME 'plugin_library';

CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20),
       species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);

CREATE TABLE test.accounts (
   id INT PRIMARY KEY AUTO_INCREMENT,
   first_name VARCHAR(25),
   last_name VARCHAR(25),
   email VARCHAR(100),
   amount DECIMAL(15,2) CHECK (amount >= 0.0),
   UNIQUE (email)
) ENGINE=InnoDB;

...
--------
FILE I/O
--------
Pending flushes (fsync): 0
295 OS file reads, 1 OS file writes, 1 OS fsyncs
0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s
...

| InnoDB |      | 
=====================================
2024-03-19 12:39:45 0x7f80f01f3700 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 43 seconds
-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 0 srv_active, 2455 srv_idle
srv_master_thread log flush and writes: 2454
----------
SEMAPHORES
----------
------------
TRANSACTIONS
------------
Trx id counter 754
Purge done for trx's n:o < 0 undo n:o < 0 state: running but idle
History list length 0
LIST OF TRANSACTIONS FOR EACH SESSION:
---TRANSACTION (0x7f8111334680), not started
0 lock struct(s), heap size 1128, 0 row lock(s)
---TRANSACTION (0x7f8111333b80), not started
0 lock struct(s), heap size 1128, 0 row lock(s)
--------
FILE I/O
--------
Pending flushes (fsync): 0
295 OS file reads, 1 OS file writes, 1 OS fsyncs
0.00 reads/s, 0 avg bytes/read, 0.00 writes/s, 0.00 fsyncs/s
---
LOG
---
Log sequence number 463193
Log flushed up to   463193
Pages flushed up to 362808
Last checkpoint at  362808
----------------------
BUFFER POOL AND MEMORY
----------------------
Total large memory allocated 167772160
Dictionary memory allocated 853016
Buffer pool size   8064
Free buffers       7647
Database pages     417
Old database pages 0
Modified db pages  164
Percent of dirty pages(LRU & free pages): 2.033
Max dirty pages percent: 90.000
Pending reads 0
Pending writes: LRU 0, flush list 0
Pages made young 0, not young 0
0.00 youngs/s, 0.00 non-youngs/s
Pages read 273, created 144, written 0
0.00 reads/s, 0.00 creates/s, 0.00 writes/s
No buffer pool page gets since the last printout
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
LRU len: 417, unzip_LRU len: 0
I/O sum[0]:cur[0], unzip sum[0]:cur[0]
--------------
ROW OPERATIONS
--------------
0 read views open inside InnoDB
state: sleeping
----------------------------
END OF INNODB MONITOR OUTPUT
============================
 |
 

/

SHOW AUTHORS GROUP BY `Location` INTO OUTFILE 'tmp.txt';

SHOW COLUMNS IN table_name WHERE (@field:=`Field`) > '';

CHECK TABLE c1, m WHERE `Msg_text` <> 'OK';

SELECT * FROM (DESCRIBE information_schema.tables) AS x ORDER BY 1;

SHOW COLLATION ORDER BY `Id` INTO OUTFILE 'tmp.txt';

SELECT `Type` FROM (SHOW COLUMNS IN Employees) AS x GROUP BY `Type`;

SELECT UPPER(`Name`) from (SHOW Contributors) as x;

SHOW ENGINES ORDER BY `Engine`;

(SELECT `Name` FROM (SHOW CONTRIBUTORS) AS x
UNION ALL SELECT `Name` FROM (SHOW AUTHORS) AS y)
ORDER BY 1;

CREATE TABLE engines AS SHOW ENGINES;

(SELECT 'Alibaba Cloud' AS `Name`, 'https://www.alibabacloud.com' AS `Location`, 'Platinum Sponsor of the MariaDB Foundation' AS `Comment")

SET OCELOT_STATEMENT_SYNTAX_CHECKER = '7';

Charts

SELECT 0,1,2,3,4,5,6,7,8; result can look like this

but should it?

I’ll try to cover here what would be an obvious way to show number columns in charts, or if not obvious then at least simple, or if not obvious or simple then at least understandable, or if none of the above, well, good looking.

The initial part of this description will look a bit like what you see with DB2 magic commands for bar or line or pie charts, but I like to think the later part of this description shows something more sophisticated.

Bars

Start with the most obvious: any group of numbers can be shown as a group of bars.

Should they be horizontal by default? That appears to be the less common choice, A Complete Guide to Bar Charts says “While the vertical bar chart is usually the default …”, ChartJs says “The default for this property is ‘x’ and thus will show vertical bars.”

But a SAS blog 3 reasons to prefer a horizontal bar chart persuaded me because, when we’re a GUI displaying an SQL result set, we usually have more room on the x (width) axis than on the y (height) axis.

Now, as for simpleness: that should mean there’s no extra work or time for exporting, manipulating in a non-SQL environment, learning Python, or even having to think — if the total time including user time is more than a second, that’s a fail. Therefore it has to be possible to get
SELECT 1,2,3;
which ordinarily displays as

to display as

with a shortcut that includes a mnemonic. Therefore hitting Alt+Shift+B should switch immediately to the bar-chart display.

But it can get more complex, and that means users must enter instructions, and the only way to make that simpler is to provide instruction syntax that looks like SQL, thus:

SET ocelot_grid_chart = 'bar vertical';

… since users will know that SET value = literal is the SQL way to assign, and will know that ''s enclose literals, and will know what vertical means. So this is the result and it won’t be surprising:

Another bar-chart variant is stacking, that is, putting 3 values in one bar instead of 3 side-by-side bars. For example

SET ocelot_grid_chart = 'bar stacked';

or

SET ocelot_grid_chart = 'bar vertical stacked';

Lines

Lines are a bit less obvious than bars, because if there’s only one number in the series, they’re meaningless. Nevertheless, there should be a simple way to show a chart. Therefore Alt+Shift+L will cause

x

Maybe, although I suppose everyone has seen this sort of thing before, I should make some terminology notes around now …
X-axis: usually this is the horizontal, with the word “samples”
Y-axis: usually this is the vertical, with the word “values”
Legend: in the upper right corner, with a colour icon and a short indicator
Ticks: the tiny marks along the values, so users can see what the scale is.

For the French terms, see Statistique Canada.

But if users don’t know the terms, that’s fine, they understand the picture anyway.

Pies

Pies are obvious and simple too, all they require is
Alt+Shift+P or

SET ocelot_grid_chart='pie';

and SELECT 1,2,3; will look like this:

Fine. But putting numbers along the x-axis and y-axis wouldn’t be informative, and nobody has figured out what should happen with negative numbers. I think Microsoft Excel would take the absolute value, I think it makes more sense to ignore, but the point is: no solution is intuitive for all, therefore there’s a gotcha, therefore it’s not obvious and simple after all.

Groups

Every illustration so far has been simple, a 3-number series. There’s no complicated decision-making, the algorithm is just “if it’s a number, i.e. any of the data types that the DBMS fits in a general numeric category, it’s in, otherwise it’s out”.
It would follow, then, that

>SELECT 1,2,3,'',4,5,6,'',7,8,9;

would result in this if the setting was for bar charts:

There are three “groups” here, and “groups” is a better word than “series” because GROUP is an SQL-standard term.

Subgroups

Now things get a bit more complex. What makes us decide that every individual numeric-column occurrence should be part of a separate bar or line or pie segment? Answer: nothing does, that’s simple but not really the best for representing some of the typical chart situations.

Take the possibility that all the columns which have something in common are combined. The commonness could be the value. For example

SET ocelot_grid_chart='bar vertical subgroup by value % 3';

SELECT 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15;

That is, the values which are divisible by 3 are together, but distributed across the landscape. Each of the things that are together are usually called “samples” if one uses chart terminology, and that’s why in this illustration the word “samples” appears at the bottom, and each subgroup has a separate colour, which is echoed by the legend.

More usefully, I think, the commonness could be the column_name prefix. The usefulness lies in the fact that users know how to put AS clauses after column names in the select list, so they can determine what the subgroups are. For example

SET ocelot_grid_chart='bar vertical subgroup by left(column_name, 1)';

SELECT 1 AS x_1, 2 AS y_1, 3 AS z_1, 4 AS x_2, 6 AS y_2, 7 AS z_2;

There might be other criteria for deciding how to subgroup, but they’re probably less important. What’s important is that once again the syntax is something any SQL user will understand.

Actually the word that chart-lovers prefer here is “categories”, and “subgroups” isn’t really a word you’ll find in typical SQL, but at the moment I’m thinking it’s “SQL-ish”.

Nulls

Since this is SQL, NULLs exist.

There’s no such thing as obvious when NULL might mean unknown or inapplicable, but this isn’t Oracle so it would be too trite to say NULLs are zeros, at least when it’s possible to hint otherwise. Thus

SET ocelot_grid_chart='bar vertical subgroup by left(column_name, 1)';

SELECT 1 AS m, 2 AS m, 3 AS m, 4 AS o, 5 AS o, NULL AS o;

doesn’t use a solid colour, but has the same size as whatever the largest bar is.

I worry that by now we’ve evolved from “obvious” to merely “understandable”, so I’ll explain this example more deeply. In this example there are three samples of ‘m’ and ‘o’. The first sample, label 0, has the first ‘m’ and it has value = 1, the black bar, and it has the first ‘o’ and it has value = 4, the red bar. Sample 1 has the second ‘m’ and the second ‘o’. Sample 2 has the third ‘m’ and ‘o’, and, since the third ‘o’ is NULL, it is not solid. The legend in the right corner is helpful for showing that
black is ‘m’ and red is ‘o’.

WHERE clauses

But surely not every numeric column should always be in a chart? I think of column names that end with ‘_id’, or the possibility that one will want to display both the chart and the numbers as text.

The SQL syntax for deciding what’s in a group could be CASE … WHEN, or IF … THEN, but what even the novice SQL user has seen is WHERE. The condition could be COLUMN_NAME relative-operator value, COLUMN_NUMBER relative-operator value, COLUMN_TYPE relative-operator value. By the way, since this is a GUI, users will see hints for autocompletion when they type WHERE, for example

and after

SET ocelot_grid_chart='bar vertical stacked' WHERE column_type = 'integer';

SELECT 1,1.1,2,7,-44;

the result will not include 1.1 in a chart because it is not an integer.

And this is where it becomes possible at last to show the statements that caused the example at the start of this post, where some of the columns were in a bar chart, some in a line chart, and some in a pie.

SET ocelot_grid_chart = 'line' WHERE column_number <= 3;
SET ocelot_grid_chart = 'bar' WHERE column_number >= 4 AND column_number <= 6;
SET ocelot_grid_chart = 'pie' WHERE column_number > 6;
SET ocelot_grid_chart = '' WHERE column_number > 100;
SELECT 0,1,2,3,4,5,6,7,8;

and we’ve arrived at the example we started with.

Turning it off

Alt+Shift+N or

SET ocelot_grid_chart='';

will erase all earlier chart statements. So there’s a simple way to go back to the regular way to display results.

Source Code

My main purpose describing all this is to show what the design of a GUI should look like, if my observations about goals make sense.

The illustrations show what the implementation looks like as of today, they’re screenshots of ocelotgui, and they work as I’ve described. But currently they’re only distributed in source code. Anyone who wants to reproduce them today can download the source from github, follow the special build instructions in file chart_options.txt, connect to MySQL or MariaDB or Tarantool, and see the same things. You will notice that you need to use the Qwt library, which should be no problem (ocelotgui is GPLv2, Qwt is LGPL, Qwt is on many distros). Pay no attention to the bug in the room.

But I’m not sure whether to call this the final look for the next executable release. Let me know in the comments if I’m missing tricks.

Delimiters in MySQL and MariaDB

In the SQL standard delimiters are for separating tokens; in MySQL/MariaDB they’re for ending statements, particularly compound statements as in

CREATE PROCEDURE p()
BEGIN
  VALUES (5);
END;

The problem is that a dumb client could stop at the first semicolon “;” in the statement (the one after VALUES (5)) instead of the one that truly ends (the one after END). The solution is to say that semicolon is no longer the default delimiter, and the way to specify a replacement is with a non-standard DELIMITER statement, such as

DELIMITER //

and after that the true statement end is //.

The idea isn’t unusual — in PostgreSQL’s psql client you can enclose compound statements with $$ which they call dollar quoting, with Microsoft you get used to saying “go” when you want something shipped to the server, with Oracle you might sometimes see SQLTERMINATOR. But it shouldn’t always be necessary — despite the fact that words like BEGIN are not reserved, a client with even a slight ability to recognize syntax can see where a compound statement ends without needing special tags.

Quirks

Some DELIMITER quirks are documented in either the MySQL manual or MariaDB manual, some are common to all mysql-client commands, but all are weird. They are:
() DELIMITER itself is not delimited
() After DELIMITER A B the delimiter is A
() After DELIMITER A; the delimiter is A;
() After DELIMITER 12345678901234567890 the delimiter is 123456789012345
() After DELIMITER ‘x’ or DELIMITER “x” or DELIMITER `x` the delimiter is x
() After DELIMITER ;; the delimiter is ;;
() Delimiters inside comments or character string literals or delimited identifiers are ignored
() After \dA the delimiter is A (\d is a substitute for DELIMITER and no space is necessary)
() After DELIMITER \ the effect can be odd, the MySQL manual recommends not to use \
() SELECT 5; DELIMITER ; will cause an error message
() DELIMITER ;; followed by SELECT 5;;; has a different effect from DELIMITER // followed by SELECT 5;//
() \G and \g will work whether or not there is a delimiter

It is not a gotcha that, when statements are in a .sql file and read by the SOURCE file-name statement, the rules are different: Compound statements will be recognized without special delimiters, and semicolons will always end non-compound statements even after a different delimiter has been specified.

It is not a quirk or a gotcha, it’s merely bad design, that DELIMITER forces the fundamental requirement of a parser — the tokenizer — to change what the tokenizing rules are while the tokenizing is going on.

Best practice

Both the MySQL and the MariaDB manual have example statements where the delimiter is // and that’s unlikely to cause confusion, since the only other uses of / are as a beginning of a bracketed comment or as a division operator, or in arguments to PROMPT or SOURCE or TEE.
Less frequently there is a recommendation for $$ but that is bad because $$ can occur inside regular identifiers.
DELIMITER !! is equally bad because !, unlike /, is a repeatable operator, for example SELECT !!5; returns 1.
DELIMITER ;; is worse and has caused bugs in the past, but the mysqldump utility will generate it before CREATE TRIGGER statements.

Avoid non-printable or non-ASCII characters, some clients will support them but others won’t.

You could set a delimiter at the start of a session and let it persist. But I believe the more common practice is to put DELIMITER [something appropriate] immediately before any CREATE PROCEDURE or CREATE TRIGGER or CREATE FUNCTION or BEGIN NOT ATOMIC statement, and DELIMITER ; immediately after. This might help readability by humans since otherwise they’d look at statements that end with mere semicolons and assume they’d go to the server immediately, not realizing that long ago there was a DELIMITER statement.

See also the Descriptive SQL style guide section “Semicolons”.

ocelotgui

The ocelotgui client doesn’t need DELIMITER statements because obviously a client that includes a stored-procedure debugger can recognize compound statements, but it will accept them because it tries to be compatible with the mysql client. It does not duplicate mysql client behaviour for the SOURCE statement but that should be fixed in the next version, and the fix is now in the source code which can be downloaded from github.

ocelotgui version 1.7

Version 1.7 of ocelotgui has these changes.

Bug fix: due to a recent MariaDB change, our stored-procedure debugger could not be installed when connecting to a MariaDB server (MySQL debugging was not affected). Now all is well again.

Here, for example, is a screenshot of ocelotgui after connecting to MariaDB 10.8, saying $debug P; and then Alt+5 (“Step”) 4 times, then clicking menu item “Refresh user variables” to see the previous and current values of @a:

/

Incidentally I’ve just noticed some old comments about ocelotgui on https://stackoverflow.com/questions/3007625/mysql-stored-procedure-debugging with one user saying “… helped me a lot!” and another saying “I connected, debugged their tutorial, and am amazed. it’s a GREAT step debugger with variable data view on demand. lots to learn, but the #1 choice so far for free.” Don’t get the wrong idea though — debugging is a unique feature but not the major one.

New platform: Actually ocelotgui runs on any Linux distro (and Windows of course); however, the only specific instructions for creating packages were ones for .deb (Debian-based) and .rpm (Red-Hat-based). Now there is a script file for creating packages on Arch-Linux-based distros too, for example Manjaro or EndeavourOS. It’s PKGBUILD.

Enhancement: Detaching wasn’t quite as spiffy as it should be because our size calculations were slightly wrong. Here’s a screenshot showing the same widgets as before, after detaching them all and doing some manual fiddling:

As usual, downloads and executables are available on our github repository.

Autocompletion with the mysql client

The concept of autocompletion is old and simple. You type some characters; the program shows some choices for what characters might follow; you can choose a choice by hitting a special key. It can save on typing, and save on looking up in dictionaries or information schemas.

I will illustrate what the manuals mean, then show features or quirks that the manuals fail to say, then compare with a GUI.

The Example

For The Example, I used MySQL 8.0 mysql client and MariaDB 10.5 mysql client, on Linux. I understand that they work on Windows 10 if you install a Linux shell.

You should find it easy to follow along with your own copy of mysql client, even if you started with non-default options and have minimal privileges.

The first thing to do is declare a “current database” with USE, and say that you want to enable autocompletion with REHASH.
I’ll discuss later why these might be unnecessary statements, but there’s no harm in making sure.

USE information_schema;
REHASH;

Now type lo then type the [Tab] key twice. Your screen will look like this:

Now type the [Backspace] key twice, then type LO, then type the [Tab] key twice. Your screen will look like this (the items might be in a different order depending on the server):

Now type the [Backspace] key twice, then type LOCALTIMEST, then type the [Tab] key once. Your screen will look like this:

At this point you have probably figured out these things:
* Searching is case sensitive, lo and LO are different
* If there is more than one choice, [Tab] [Tab] causes a display
* If there is only one choice, [Tab] causes a replacement
* Context is irrelevant, most of the choices would be illegal as statement start
* Choices include table names, column names, and keywords.

To complete what you could figure out, you could try these additional tests:
inf [Tab] [Tab] — you’ll see information_schema because choices also include database names
BEG [Tab] [Tab] — you’ll see BEGIN because choices also include non-reserved keywords
INF [Tab] [Tab] — there will be a question whether you want to see all choices because 100+ choices may not be a useful hint.

Command line options

To back up a bit, the reason that the USE and REHASH statements might have been unnecessary is that there might be defaults.

If you started mysql with --database=database_name or -D database_name, then USE is automatic when you connect.

If you started mysql with –auto_rehash, or you just omitted the option because it is default default, then REHASH is automatic when you USE.

Do not let the “auto” in “–auto-rehash” deceive you too much though. REHASH will not happen automatically if anyone changes the current database with CREATE or DROP or ALTER. REHASH will not happen automatically if you say USE x; when x is already the default database.

So if you worry about depending on obsolete choices, you will need to do manual REHASHes occasionally.

The REHASH Statement

prompt> REHASH; /* or /# */

REHASH is not a good name — it hints about how the job is implemented, rather than what it does, which is: select the names of databases, names of tables (both base tables and viewed tables but not temporary tables) in the current database, names of columns of those tables, keywords (both reserved words and unreserved words), and names of mysql commands. Completion will not work if REHASH has not happened, not even for keywords.

REHASH will not select names of tables that you don’t have privileges for. There is a small security breach though: If you have a column-level privilege for any column in the table, then the menu choices will include all columns in the table, including the ones you don’t have privileges for. (In theory you are not supposed to know about such columns, which is why you won’t see them in information_schema.)

Unlike USE, which tells you “Reading table information for completion of table and column names”, REHASH gives no feedback. But it does succeed. If you have only a few thousand tables and columns, it takes negligible time.

What library mysql is using

For most editing operations, including [Tab] handling, the mysql client passes off the work to an open-source library, either readline or libedit.

If you have an old MySQL version, or if you have MariaDB, your mysql client probably has readline. One way to tell is to say

mysql --help | grep readline

Any non-blank response, for example

mysql  Ver 15.1 Distrib 10.1.47-MariaDB,
for debian-linux-gnu (x86_64)
using readline 5.2

indicates that your mysql client has readline. Alternatively you could say “whereis mysql … ldd mysql-location” and look for libreadline.so in the output.

If you have MySQL 5.6.5 or later, your mysql client almost certainly has bundled libedit. (In version 5.5 there was still a CMake option -DWITH_READLINE=1, but it is gone now.) If you have MariaDB, your mysql client probably does not have libedit unless you built from source and passed the -DWITH_LIBEDIT option to cmake. One way to tell is to create a file named ~/.editrc and insert this temporary line:

mysql:bind

(If the file already exists, no problem, just add a line saying mysql:bind at the start.) Now start the mysql client. If it displays a list titled “Standard key bindings”, then your client has libedit. Specifically it is close to the NetBSD variation of libedit. Now remove the line saying mysql:bind from libedit.

It has been suggested that MySQL/Oracle’s changed preference was due more to licence considerations than to features (readline is GPL and libedit is BSD), and indeed it is true that there are more things you can do with autocompletion if you use the mysql client from MariaDB, as we will see.

Today (November 6 2020) the MySQL 8.0 manual still has mentions of readline, here and here and here. They are obsolete, ignore them.

Using a different key instead of [Tab]

The special key for completion is [Tab] so sometimes autocompletion is called “tab completion”. But it doesn’t have to be. You can change the “key binding” — the way that a particular key is connected to a particular operation — by changing a file that the library reads when you start the mysql client. There is no denying that [Tab] is the more popular choice on Linux, partly because it is the default for both libedit and readline, and some Linux utilities such as bash depend on readline. But [Tab] is a displayable character so it is unusual — and I think bizarre — to see it within an application that is editing text. There is a way to say “Let [Tab] be [Tab], and use a control character for completion.”

If the library is libreadline, then the file to change is ~/.inputrc. If it does not already exist, then you can create it, but then be sure to $include /etc/inputrc at the top, otherwise the user’s copy will just override the system one. Make it look like this:

$include /etc/inputrc
Control-I: tab-insert
Control-N: complete

This would also work:

$include /etc/inputrc
TAB: self-insert
Control-N: complete

Unless you have an exotic terminal, [Tab] and Control-I have the same effect.

If the library is libedit, then the file to change is ~/.editrc and the key binding that matters for completion is rl_complete. Edit ~/.editrc again and remove the line that says bind, and add these lines:

mysql:bind "^N" rl_complete
mysql:bind "\t" ed-insert

I like it that I can specify that I only want to affect mysql.

Now start the mysql client again, and once again say

USE information_schema;
REHASH;
DROP TABLE 

and now type control-N twice. You will see that it displays exactly the same thing that you saw when you typed [Tab] twice. However, if you now type [Tab], you will get a tab.

Warning: before changing a key binding, make sure that the key is not used by other programs or has some default libreadline/libedit binding already. And check with stty -a.

Undocumented readline features

Actually these key bindings are documented for readline,
but the MySQL and MariaDB manuals don’t list them so I’m
guessing most mysql users don’t know about them. To see what the relevant key bindings are, I use bind:

$ bind -P | grep complete
complete can be found on "\C-n", "\e\e".
complete-command can be found on "\e!".
complete-filename can be found on "\e/".
complete-hostname can be found on "\e@".
complete-into-braces can be found on "\e{".
complete-username can be found on "\e~".
complete-variable can be found on "\e$".
dynamic-complete-history can be found on "\e\C-i".
glob-complete-word can be found on "\eg".
menu-complete is not bound to any keys
menu-complete-backward is not bound to any keys
old-menu-complete is not bound to any keys
vi-complete is not bound to any keys

This is rather cryptic but you probably can guess that “\C-n” means “Control-N”, which is the suggestion that I made for ~/.inputrc. However, the interesting items are menu-complete and menu-complete-backward. Let’s bind them to some keys and see what a readline-based mysql client does with them.

First change ~/.inputrc again so now it looks like this:

$include /etc/inputrc
Control-I: tab-insert
Control-N: complete
Control-J: menu-complete
Control-K: menu-complete-backward

Now start mysql again and do some of the same steps as before:

USE information_schema;
REHASH;

And now type LO and then type control-N twice
(not [Tab] any more), and you’ll see

Now type Control-J. Suddenly the word becomes the first choice
in the menu


Now type Control-J again. Now the word becomes the second choice in the menu


Keep typing Control-J and eventually readline will cycle back
to the first choice. Or type control-K and completions will be of the previous items.

This, I think, is how autocompletion should always work.
If you have a menu of choices, you should have a way to
navigate to a specific choice by typing a single key.

Try out even more behaviour changes by adding these lines at the end of ~/.inputrc:

# Case-insensitive (disabled)
set completion-ignore-case On
# Don't do anything until user types at least 3 characters (disabled)
set completion-prefix-display-length 3
# If there are more than 5 choices ask "Display all xx possibilities?"
set completion-query-items 5
# Of course disable-completion No is default
set disable-completion No
# If there are many choices don't show a page at a time and ask for "More"
set page-completions Off
# Menu options should be vertical, that would be normal (disabled)
set print-completions-horizontally No
# If there are two or more choices show them after hitting special key once
set show-all-if-ambiguous Yes
# Show what is changed (disabled)
set show-all-if-unmodified On
# If it is completed then put the cursor after it
set skip-completed-text On
# Don't hear a bell, see a bell (disabled)
set bell-style visible

These are not libedit features, but I shouldn’t omit mentioning that libedit has many other key bindings and customization chances, unrelated to autocompletion. It is not hard to use MariaDB’s mysql client to connect to MySQL’s server, but I doubt it’s worthwhile just for some extra autocomplete gizmos.

In a GUI client

It should be clear that the mysql client does an adequate autocompletion job. But I can think of many clients that do a better job, from either MySQL or third parties. I am only going to illustrate one of them — our ocelotgui — but I am not suggesting that it is unique in this respect, since any competent GUI will have at least a few of these additional features. And I am not suggesting that any one of these additional features is important — only “autocompletion” itself is important. But I think that as a whole they save some time and trouble.

You should be able to follow along with your own copy of ocelotgui, if you have downloaded the latest version from github.

Say USE information_schema and REHASH.

Change so completion is done with Alt-N rather than [Tab].

Type DROP TABLE

Move the cursor and hover, to see instructions.

Use the down-arrow to select one of the menu items.

Type Alt-N or click Autocomplete on the main Edit menu

Wait OCELOT_COMPLETER_TIMEOUT seconds for the menu to disappear.

Notice these differences …
(1) Changing [Tab] can be done within the program (although of course it can also be done by changing a file).
(2) The choices appear immediately, with a GUI there’s no need for [Tab] or a special key to make them appear.
(3) The choices include only what is relevant in context, i.e. after DROP TABLE the only possible items are IF and table names.
(4) The colour of the choices is the same as the colour of the highlighting, which is why IF (a keyword) and * (an identifier) look different.
(5) The navigation is done with arrow keys on a purely vertical menu with a scroll bar, regardless of number of choices.
(6) Hints and menu choices appear temporarily, as in IDEs.
Another difference is that this works the same way on Windows as well as Linux, out of the box.

Of course you can’t actually drop a table in information_schema, and ocelotgui will fail to warn you about that. I admit as much. “Perfection” is still on the to-do list.