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DML转select count时，如果DML带有limit，应该额外加一层select count(1) from (...... limit ...) #119

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Nov 19, 2019
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DML转select count时，如果DML带有limit，应该额外加一层select count(1) from (...... limit ...) #119

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15 changes: 14 additions & 1 deletion session/rewrite.go
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,7 @@ func delete2Select(stmt *sqlparser.Delete) string {
From: stmt.TableExprs,
Where: stmt.Where,
OrderBy: stmt.OrderBy,
Limit: stmt.Limit,
}
return sqlparser.String(newSQL)
}
Expand Down Expand Up @@ -135,8 +136,20 @@ func (rw *Rewrite) select2Count() string {
Where: stmt.Where,
GroupBy: stmt.GroupBy,
Having: stmt.Having,
Limit: stmt.Limit,
}

//fix the bug when the 'limit' we assign will not be the condition which what we exactly want
//for example we want to get the affected rows from the sql 'select * from table where id < 100 limit 10'
//before the bug fixed bug, the rewrited sql is 'select count(*) from table where id < 100 limit 10', which is incorrect
//what we exactly want is 'select count(*) from (select 1 from table where id < 100 limit 10)'
if stmt.Limit != nil {
newSQL.Limit = stmt.Limit
newSQL.SelectExprs = []sqlparser.SelectExpr{
new(sqlparser.StarExpr),
}
return fmt.Sprintf("SELECT COUNT(1) FROM (%s)t", sqlparser.String(newSQL))
}

return sqlparser.String(newSQL)
// case *sqlparser.Union, *sqlparser.ParenSelect:
// return fmt.Sprintf("SELECT COUNT(1) FROM (%s)t", rw.SQL)
Expand Down