ddl: create partition table fail with strconv.ParseInt invalid syntax

[tiancaiamao]

What problem does this PR solve?

Issue Number: close #16333

Problem Summary:

mysql> create table t (dt timestamp) partition by range (unix_timestamp(dt)) (partition p0 values less than (unix_timestamp('2020-04-15 00:00:00')));
ERROR 1105 (HY000): strconv.ParseInt: parsing "unix_timestamp(\"2020-04-15 00:00:00\")": invalid syntax

What is changed and how it works?

Proposal: xxx

What's Changed:

Fix bug

How it Works:

During the create of the table, the partition information should be convert to integer.
The 'less than xxx' part of a partition in the model should be integers.

I don't know why it's broken and which PR cause this.
4.0 is fine.

Tests

• Unit test

[tiancaiamao]

PTAL @imtbkcat @crazycs520 @jackysp

[zimulala]

LGTM

[zimulala]

Do we need to cherry-pick to v4.0?

[tiancaiamao]

Do we need to cherry-pick to v4.0?

I don't know why but this test case success in 4.0
OK, I'll cherry pick 4.0 as it's simple enough.

[tiancaiamao]

/run-all-tests

[codecov]

Codecov Report

Merging #16436 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #16436   +/-   ##
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  Coverage   80.5322%   80.5322%           
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  Files           506        506           
  Lines        136939     136939           
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  Hits         110280     110280           
  Misses        18104      18104           
  Partials       8555       8555           

[tiancaiamao]

[2020-04-16T11:14:34.916Z] [2020/04/16 19:13:48.788 +08:00] [FATAL] [terror.go:348] ["unexpected error"] [error="listen tcp 0.0.0.0:10081: bind: address already in use"] [stack="github.com/pingcap/log.Fatal\n\t/home/jenkins/agent/workspace/tidb_ghpr_build/go/pkg/mod/github.com/pingcap/log@v0.0.0-20200117041106-d28c14d3b1cd/global.go:59\ngit.luolix.top/pingcap/parser/terror.MustNil\n\t/home/jenkins/agent/workspace/tidb_ghpr_build/go/pkg/mod/github.com/pingcap/parser@v0.0.0-20200410065024-81f3db8e6095/terror/terror.go:348\nmain.createServer\n\t/home/jenkins/agent/workspace/tidb_ghpr_build/go/src/github.com/pingcap/tidb/tidb-server/main.go:630\nmain.main\n\t/home/jenkins/agent/workspace/tidb_ghpr_build/go/src/github.com/pingcap/tidb/tidb-server/main.go:182\nruntime.main\n\t/usr/local/go/src/runtime/proc.go:203"]

/run-sqllogic-test-2

[imtbkcat]

LGTM

[jackysp]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

cherry pick to release-3.0 in PR #16498

[sre-bot]

cherry pick to release-3.1 in PR #16499

[sre-bot]

cherry pick to release-4.0 in PR #16500