zhangbutao commented on code in PR #3276:
URL: https://github.com/apache/hive/pull/3276#discussion_r876791141
##########
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/dataconnector/jdbc/MySQLConnectorProvider.java:
##########
@@ -90,10 +90,20 @@ protected String getDataType(String dbDataType, int size) {
// map any db specific types here.
switch (dbDataType.toLowerCase())
{
+ case "bit":
+ return toHiveBitType(size);
default:
mappedType = ColumnType.VOID_TYPE_NAME;
break;
}
return mappedType;
}
+
+ private String toHiveBitType(int size) {
+ if (size <= 1) {
+ return ColumnType.BOOLEAN_TYPE_NAME;
+ } else {
+ return ColumnType.BIGINT_TYPE_NAME;
Review Comment:
for bit-type with size <= 1 of mysql column, users usually use this column
to express false or true, so it make sense to be recognized boolean type in
hive.
for bit-type with size >1 of mysql column, users may want to express
different semantics, eg weekly working calendar, bit(7) , and in this case we
can not simply convert bit(7) to boolean type. I convert this bit(n) to bigint
in hive, eg **b'111000' will be read as 56**.
in this pr, i added qtest to select bit datatype, but HIVE-26192 blocked
me, i hope you can give advice about HIVE-26192。
> But also to be able to read this datatype, should we read as "select
bin(col)" while reading from remote table?
I think it is diffcult and not worth to read as "select bin(col)". Becaue
if we want do this, we may need to mak type check when executing query and then
convert column type to bit. Also, hive can not recognize bit type, and i think
hive will compile failed with bit type before the query is submited to mysql.
That's just my basic thought.
In addtion, i have checked the presto and spark code. presto will convert
all bit type to bolean. Spark have the similar ideas with this pr. I think
spark idea is more reasonable.
https://github.com/trinodb/trino/blob/543ae143cadeb47ab03af4197dae9d00ff5baf7c/plugin/trino-mysql/src/main/java/io/trino/plugin/mysql/MySqlClient.java#L377-L379
https://github.com/apache/spark/blob/7309e76d8b95e306d6f3d2f611316b748949e9cf/sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala#L64-#L71
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