fix: support compatible CDC show and drop syntax

[jiangxinmeng1]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #24832

What this PR does / why we need it:

What

• Support SHOW CDC as shorthand for SHOW CDC ALL.
• Support DROP CDC <name> as shorthand for DROP CDC TASK <name>.
• Support DROP CDC IF EXISTS <name> and ignore missing CDC tasks when IF EXISTS is specified.
• Pass DropCDC.IfExists through AST, plan, compile, and frontend CDC handling paths.

Testing

• go test ./pkg/sql/parsers/dialect/mysql
• git diff --check

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[mergify]

Queued — the merge queue status continues in this comment ↓.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-06-23 02:50 UTC · Rule: main · triggered by rule Automatic queue on approval for main
• ✅ Checks passed · in-place
• ✅ Merged — 2026-06-23 04:05 UTC · at fad8d1152bc575ae18d3846d249306ba885401de · squash

This pull request spent 1 hour 14 minutes 57 seconds in the queue, including 1 hour 14 minutes 40 seconds running CI.

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  • fix: support compatible CDC show and drop syntax #25003
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  • fix: support compatible CDC show and drop syntax #25003
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