Use decimal data type for the TRUNCATE argument to address the Truncated incorrect INTEGER value: '' warning

[yahonda]

What is changed, added or deleted? (Required)

This pull request replaces the data type for the truncate argument from varchar to decimal because the current example raises the Truncated incorrect INTEGER value: '' warning.

• Current example that raises the Truncated incorrect INTEGER value: '' warning.

mysql> use test;
Database changed
mysql> create table t(id int primary key, a varchar(10) not null);
Query OK, 0 rows affected (0.07 sec)

mysql> desc select * from t where truncate(a, " ") = '1';
+-------------------------+----------+-----------+---------------+---------------------------------------------------+
| id                      | estRows  | task      | access object | operator info                                     |
+-------------------------+----------+-----------+---------------+---------------------------------------------------+
| Selection_5             | 8000.00  | root      |               | eq(truncate(cast(test.t.a, double BINARY), 0), 1) |
| └─TableReader_7         | 10000.00 | root      |               | data:TableFullScan_6                              |
|   └─TableFullScan_6     | 10000.00 | cop[tikv] | table:t       | keep order:false, stats:pseudo                    |
+-------------------------+----------+-----------+---------------+---------------------------------------------------+
3 rows in set, 2 warnings (0.00 sec)

mysql> show warnings;
+---------+------+------------------------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                                                                      |
+---------+------+------------------------------------------------------------------------------------------------------------------------------+
| Warning | 1292 | Truncated incorrect INTEGER value: ''                                                                                        |
| Warning | 1105 | Scalar function 'truncate'(signature: TruncateReal, return type: double) is not supported to push down to storage layer now. |
+---------+------+------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

mysql>
mysql> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v8.1.0
Edition: Community
Git Commit Hash: 945d07c5d5c7a1ae212f6013adfb187f2de24b23
Git Branch: HEAD
UTC Build Time: 2024-05-21 03:52:40
GoVersion: go1.21.10
Race Enabled: false
Check Table Before Drop: false
Store: tikv
1 row in set (0.00 sec)

mysql>

• Updated example that does not raise the Truncated incorrect INTEGER value: '' warning.

mysql> drop table t;
Query OK, 0 rows affected (0.19 sec)

mysql> create table t(id int primary key, a decimal(10, 2) not null);
Query OK, 0 rows affected (0.07 sec)

mysql> desc select * from t where truncate(a, 0) = 1;
+-------------------------+----------+-----------+---------------+--------------------------------+
| id                      | estRows  | task      | access object | operator info                  |
+-------------------------+----------+-----------+---------------+--------------------------------+
| Selection_5             | 8000.00  | root      |               | eq(truncate(test.t.a, 0), 1)   |
| └─TableReader_7         | 10000.00 | root      |               | data:TableFullScan_6           |
|   └─TableFullScan_6     | 10000.00 | cop[tikv] | table:t       | keep order:false, stats:pseudo |
+-------------------------+----------+-----------+---------------+--------------------------------+
3 rows in set, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+---------------------------------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                                                                               |
+---------+------+---------------------------------------------------------------------------------------------------------------------------------------+
| Warning | 1105 | Scalar function 'truncate'(signature: TruncateDecimal, return type: decimal(8,0)) is not supported to push down to storage layer now. |
+---------+------+---------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>

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

• This PR is translated from:
• Other reference link(s): The current change has been made via Fix doc wrong related with substring which can be pushed down now #13682

This document says "Truncate to specified number of decimal places".
https://docs.pingcap.com/tidb/stable/numeric-functions-and-operators

TRUNCATE() Truncate to specified number of decimal places

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

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[Oreoxmt]

@xzhangxian1008 Could you please help review this PR? Thanks! This example is introduced in pingcap/docs-cn#14054