schema: sequence should always be the one row

[AilinKid]

Signed-off-by: ailinkid 314806019@qq.com

What problem does this PR solve?

Issue Number: close #30786 and #CI test failure

Problem Summary:

[2021-12-16T05:18:24.991Z] ----------------------------------------------------------------------
[2021-12-16T05:18:24.991Z] FAIL: infoschema_reader_test.go:957: testInfoschemaTableSuite.TestSequences
[2021-12-16T05:18:24.991Z] 
[2021-12-16T05:18:24.991Z] infoschema_reader_test.go:966:
[2021-12-16T05:18:24.991Z]     tk.MustQuery("SELECT TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME , TABLE_TYPE, ENGINE, TABLE_ROWS FROM information_schema.tables WHERE TABLE_TYPE='SEQUENCE' AND TABLE_NAME='seq2'").Check(testkit.Rows("def test seq2 SEQUENCE InnoDB 1"))
[2021-12-16T05:18:24.991Z] /home/jenkins/agent/workspace/tidb_ghpr_unit_test/go/src/github.com/pingcap/tidb/util/testkit/testkit.go:67:
[2021-12-16T05:18:24.991Z]     res.c.Assert(resBuff.String(), check.Equals, needBuff.String(), res.comment)
[2021-12-16T05:18:24.991Z] ... obtained string = "[def test seq2 SEQUENCE InnoDB 9]\n"
[2021-12-16T05:18:24.991Z] ... expected string = "[def test seq2 SEQUENCE InnoDB 1]\n"
[2021-12-16T05:18:24.991Z] ... sql:SELECT TABLE_CATALOG, TABLE_SCHEMA, TABLE_NAME , TABLE_TYPE, ENGINE, TABLE_ROWS FROM information_schema.tables WHERE TABLE_TYPE='SEQUENCE' AND TABLE_NAME='seq2', args:[]
[2021-12-16T05:18:24.991Z] 

What is changed and how it works?

sequence count should always be the one row rather than according to the stats info.

Check List

Tests

• Unit test

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• bb7133
• hawkingrei

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[tangenta]

Should we disable the statistics on the sequence tables?

[AilinKid]

Should we disable the statistics on the sequence tables?

any usage base? maybe we should

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/6e23914beb7a81e7823ab7672b31e60da59a06fd

[hawkingrei]

LGTM

[AilinKid]

/merge

[ti-chi-bot]

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

Commit hash: cd9fadb

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