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Mysql unparser cast targets - #26888
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Thanks @hozan23, I leave some suggestions below. Postgres also doesn't support unsigned types, so in the future we can use these new overrides to fix it.
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Thanks @nuno-faria for the review, I have combined the tests as you suggested. I agree we can use these new overrides for Postgres as well. |
…MySQL MySQL's CAST does not accept SMALLINT, TINYINT UNSIGNED, SMALLINT UNSIGNED, INTEGER UNSIGNED or BIGINT UNSIGNED as target types, but arrow_dtype_to_ast_dtype hard-coded them for Int16 and UInt8..UInt64, so MySqlDialect could not override them and the generated SQL failed with ERROR 1064.
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Which issue does this PR close?
Rationale for this change
MySQL's
CASTdoes not acceptSMALLINTor the... UNSIGNEDinteger types as target types, butarrow_dtype_to_ast_dtypehard-codes them forInt16andUInt8..UInt64. As a result,MySqlDialectcannot override them and the generated SQL fails withERROR 1064.See https://dev.mysql.com/doc/refman/8.0/en/cast-functions.html#function_cast
Checked against MySQL 8.0.46 and 8.4.13 with
SELECT CAST('1' AS <type>): every type in the issue table fails withERROR 1064, whileSIGNEDandUNSIGNEDsucceed.What changes are included in this PR?
Dialecthooksint16_cast_dtypeanduint8/uint16/uint32/uint64_cast_dtype. Their defaults return the previous types.MySqlDialectreturnsSIGNEDforInt16andUNSIGNEDfor the unsigned types.This builds on #26883.
What is the testing strategy for this PR?
New unit tests in
datafusion/sql/src/unparser/expr.rs:mysql_int16_and_unsigned_casts: the new MySQL outputdefault_dialect_int16_and_unsigned_casts: the default output is unchangedcustom_dialect_int16_and_unsigned_casts: the builder settersAre there any user-facing changes?
With
MySqlDialect,Int16casts now unparse asSIGNEDand unsigned integer casts asUNSIGNED.