IMPORT INTO autodetect file format and wildcards for file path

[alastori]

What is changed, added or deleted? (Required)

• Format detection based on file extensions (.csv, .sql, .parquet) for IMPORT INTO jobs.
• An explicit note is added to clarify that each IMPORT INTO job must target one file format; wildcards that match mixed extensions fail the pre-check and require separate jobs.
• It is explained that compression suffixes (.gz, .zstd, .snappy, …) are ignored when TiDB infers the file format.
• Minor wording clean-ups for consistency.

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

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• [ ] master (the latest development version)
• [x] v9.0 (TiDB 9.0 versions)
• [ ] v8.5 (TiDB 8.5 versions)
• [ ] v8.4 (TiDB 8.4 versions)
• [ ] v8.3 (TiDB 8.3 versions)
• [ ] v8.1 (TiDB 8.1 versions)
• [ ] v7.5 (TiDB 7.5 versions)
• [ ] v7.1 (TiDB 7.1 versions)
• [ ] v6.5 (TiDB 6.5 versions)
• [ ] v6.1 (TiDB 6.1 versions)
• [ ] v5.4 (TiDB 5.4 versions)

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

• This PR is translated from: https://github.com/pingcap/docs-cn/pull/20496 (partially)
• Other reference link(s): https://github.com/pingcap/tidb/pull/59543

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

[alastori]

@River2000i for technical review.

[ti-chi-bot[bot]]

@River2000i: adding LGTM is restricted to approvers and reviewers in OWNERS files.

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[ti-chi-bot[bot]]

@lilin90: Your lgtm message is repeated, so it is ignored.

In response to this:

/lgtm

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-11-10 08:25:21.683410503 +0000 UTC m=+690571.126440372: :ballot_box_with_check: agreed by lilin90.
• 2025-11-14 00:39:45.632602979 +0000 UTC m=+1008235.075632859: :ballot_box_with_check: agreed by hfxsd.

[lilin90]

/approve

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lilin90

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• ~~OWNERS~~ [lilin90]

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