data-type-string: Corrections

[dveeden]

What is changed, added or deleted? (Required)

• Add remark about default row/column sizes for types that are over the default 6 MiB.
• Correct the text for TEXT(M)

From the mysql docs on string data types:

An optional length M can be given for this type. If this is done, MySQL creates the column as the smallest TEXT type large enough to hold values M characters long.

sql> CREATE TABLE t1 (id int primary key, c1 TEXT(60), c2 TEXT(70), c3 TEXT(70) CHARSET ASCII);
Query OK, 0 rows affected (0.1513 sec)

sql> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int(11) NOT NULL,
  `c1` tinytext DEFAULT NULL,
  `c2` text DEFAULT NULL,
  `c3` tinytext CHARACTER SET ascii COLLATE ascii_bin DEFAULT NULL,
  PRIMARY KEY (`id`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
1 row in set (0.0003 sec)

sql> CREATE TABLE t1 (id int primary key, c1 TEXT(0));
ERROR: 1050 (42S01): Table 'test.t1' already exists

So:

• TEXT(60) results in TINYTEXT (60×4=240, which is less than 255)
• TEXT(70) results in TEXT (70×4=280, which is more than 255)
• TEXT(70) CHARACTER SET ASCII results in TINYTEXT (70×1=70, which is less than 255)

sql> CREATE TABLE t2 (id int primary key, c1 TEXT(0));
Query OK, 0 rows affected (0.1293 sec)

sql> INSERT INTO t2 VALUES (1, 'some text');
Query OK, 1 row affected (0.0112 sec)

sql> TABLE t2;
+----+-----------+
| id | c1        |
+----+-----------+
|  1 | some text |
+----+-----------+
1 row in set (0.0011 sec)

sql> SHOW CREATE TABLE t2\G
*************************** 1. row ***************************
       Table: t2
Create Table: CREATE TABLE `t2` (
  `id` int(11) NOT NULL,
  `c1` tinytext DEFAULT NULL,
  PRIMARY KEY (`id`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
1 row in set (0.0003 sec)

This is to show that a TEXT(0) can actually hold a string of 9 characters (and 9 bytes).

sql> CREATE TABLE t3 (id int primary key, c1 TEXT(4294967296));
ERROR: 1439 (42000): Display width out of range for column 'c1' (max = 4294967295)

sql> CREATE TABLE t3 (id int primary key, c1 TEXT(4294967295));
Query OK, 0 rows affected (0.1685 sec)

This error says this is the display width, but I don't think that's really true as that is only used for integer types.

Closes #4014

Which TiDB version(s) do your changes apply to? (Required)

• master (the latest development version)
• v6.4 (TiDB 6.4 versions)
• v6.3 (TiDB 6.3 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):
  • tidb-configuration-file: add more notes to txn-entry-size-limit #10629

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn
• tangenta

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[TomShawn]

LGTM

[TomShawn]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ceb8da0

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #11255.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #11256.