[Fix-18391] [Alert] Use lowercase table name in information_schema query for PostgreSQL compatibility

[njnu-seafish]

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Purpose of the pull request

close #18391

Brief change log

Use lowercase table name in information_schema query for PostgreSQL compatibility.

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If your pull request contains incompatible change, you should also add it to docs/docs/en/guide/upgrade/incompatible.md

[njnu-seafish]

I noticed the information_schema SQL style is a bit inconsistent right now. PostgreSQL uses lowercase table names, but MySQL mixes upper and lower case (because MySQL is case-insensitive). Should we unify everything to lowercase for better cross-database compatibility? @SbloodyS

[SbloodyS]

Not all mysql will be case sensitive. This needs to distinguish between mysql and postgres.

[njnu-seafish]

Not all mysql will be case sensitive. This needs to distinguish between mysql and postgres.

I've tested this on both MySQL 5.x and 8.x, and both information_schema.tables and information_schema.TABLES execute without any issues.

I don't have the environment to test every version of MySQL and PostgreSQL, so I asked an AI this question: For information_schema.tables and information_schema.TABLES, which casing should I use to ensure compatibility with both MySQL and PostgreSQL?

-------------------------------Here is the AI's answer:-----------------------------------
To ensure compatibility across both MySQL and PostgreSQL, it is highly recommended to use lowercase (i.e., information_schema.tables).
Here is the breakdown of why lowercase is the best choice:

1. PostgreSQL's Default Behavior
   PostgreSQL automatically folds (converts) unquoted identifiers to lowercase. So, whether you write information_schema.tables or information_schema.TABLES, PostgreSQL treats them exactly the same. Using lowercase aligns perfectly with PostgreSQL's internal logic and standard conventions.
2. MySQL's Compatibility
   MySQL fully supports lowercase information_schema.tables. While MySQL 8.0 treats INFORMATION_SCHEMA as case-insensitive, older versions (like MySQL 5.x on Linux) can be case-sensitive depending on the OS file system and the lower_case_table_names setting. Lowercase is universally safe.
3. The Risk of Using Uppercase
   While uppercase works in most cases, it can cause issues if someone accidentally uses double quotes. In PostgreSQL, double quotes force strict case sensitivity (e.g., "INFORMATION_SCHEMA" is different from information_schema). Sticking to lowercase avoids this trap entirely.
   Best Practice for Cross-Database Scripts:
   When writing SQL that needs to run on multiple database engines, always use lowercase for both the schema name, table names, and column names (e.g., SELECT table_name FROM information_schema.tables WHERE table_schema = 'my_db';).