types: fix delete error when convert string to float or int

[DQinYuan]

What problem does this PR solve?

To fix the issue #10806

When delete from a varchar column only with empty string and a condition compare with a integer or float, tidb will return a "Data Truncated Error" and mysql(both 5.x and 8.x) will only return "Query OK, 0 rows affected (0.01 sec) "

What is changed and how it works?

Before:

tidb>create table t (a varchar(30));
tidb>insert into t values ('');
tidb>delete from t where a=10;
ERROR 1265 (01000): Data Truncated

After:

tidb>create table t (a varchar(30));
tidb>insert into t values ('');
tidb>delete from t where a=10;
Query OK, 0 rows affected (0.01 sec) 

modify method getValidFloatPrefix in types/convert.go

When stmt context is "delete"(i.e. sc.InDeleteStmt is true) and string is empty, getValidFloatPrefix directly return "0" and nil error.

func getValidFloatPrefix(sc *stmtctx.StatementContext, s string) (valid string, err error) {
	if sc.InDeleteStmt && s == "" {
		return "0", nil
	}
......

Check List

Tests

• Unit test

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #10861 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #10861   +/-   ##
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  Coverage   81.2876%   81.2876%           
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  Files           423        423           
  Lines         90133      90133           
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  Hits          73267      73267           
  Misses        11561      11561           
  Partials       5305       5305

[alivxxx]

LGTM

[winkyao]

This function is used in StrToUint, maybe not only delete statement?

[DQinYuan]

The condition statementContext.InDeleteStmt == true will keep it only work in delete statement.

And in delete statement, empty string can always convert to 0 without error and warning.(according to behaviour of mysql 5.x and 8.x ).

But in other statement like select, tidb is consistent with mysql(all with warning), so I restrict it in delete statement context.

[Deardrops]

I suggest do not add more parameter for func testStrToFloat, considering 2 points:

1. This new parameter inDeleteStmt only use in one test case - String is empty. We don't need to bring this parameter to other test case, which is this PR has done.
2. The test cases of TestStrToInt and TestStrToUInt are missing. According to the Issue's description Inconsisitent with Mysql When a varchar column only have empty string #10806, we actually need these test case.

In my view, we could add a new test function for the case of this issue

func testDeleteEmptyStringError(c *C) {
	sc := new(stmtctx.StatementContext)
	sc.InDeleteStmt = true

	str := ""
	expect := 0

	val, err := StrToInt(sc, str)
	c.Assert(err, IsNil)
	c.Assert(val, Equals, int64(expect))

	val1, err := StrToUint(sc, str)
	c.Assert(err, IsNil)
	c.Assert(val1, Equals, uint64(expect))

	val2, err := StrToFloat(sc, str)
	c.Assert(err, IsNil)
	c.Assert(val2, Equals, float64(expect))
}

and call the new test function in the end of func TestStrToNum

	testStrToFloat(c, "-1e649", -math.MaxFloat64, true, ErrTruncatedWrongVal)
	testStrToFloat(c, "-1e649", -math.MaxFloat64, false, nil)

+	// for issue #10806
+	testDeleteEmptyStringError(c)
}

[DQinYuan]

@Deardrops You are right, I have corrected unit test in this pr.

[Deardrops]

LGTM

[zz-jason]

LGTM

[zz-jason]

@DQinYuan Sorry for the late review. Could you update the PR with the latest master branch and resolve the conflicts?

[zz-jason]

LGTM