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Posted to reviews@spark.apache.org by "yaooqinn (via GitHub)" <gi...@apache.org> on 2024/04/09 10:15:04 UTC
[PR] [SPARK-47781][SQL] Handle negative scale and truncate exceed scale first for JDBC data sources [spark]
yaooqinn opened a new pull request, #45956:
URL: https://github.com/apache/spark/pull/45956
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SPARK-30252 has disabled the definition of the negative scale for decimals. It has a regression that also disabled reading negative scale decimals from data sources. **Although there is a legacy config to restore the old behavior**, it seemed neither designed for such a case, nor convenient in a data pipeline that extracts negative scale decimals from a database such as Oracle to Parquet files w/o negative scale decimal support.
In addition, Postgres has the negative scale decimals support since v15, which was one of the supporters for disabling negative scale decimals on our side.
In this PR, we change the schema from `decimal(p,s)` to `decimal(p-s,0)` if s<0.
This PR also follows SPARK-45905 (#43781) to prefer to retain integral digits rather than decimal digits when reading decimals with exceeded precisions
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Negative scale decimals have many supporters for rounding the internal parts, such as Oracle, Postgres, etc.
- Oracle
> Negative scale is the number of significant digits to the left of the decimal point, to but not including the least significant digit. For negative scale the least significant digit is on the left side of the decimal point, because the actual data is rounded to the specified number of places to the left of the decimal point. For example, a specification of (10,-2) means to round to hundreds.
- Postgres
> Beginning in PostgreSQL 15, it is allowed to declare a numeric column with a negative scale. Then values will be rounded to the left of the decimal point. The precision still represents the maximum number of non-rounded digits. Thus, a column declared as
NUMERIC(2, -3)
will round values to the nearest thousand and can store values between -99000 and 99000, inclusive. It is also allowed to declare a scale larger than the declared precision. Such a column can only hold fractional values, and it requires the number of zero digits just to the right of the decimal point to be at least the declared scale minus the declared precision. For example, a column declared as
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new tests
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Re: [PR] [SPARK-47781][SQL] Handle negative scale for JDBC data sources [spark]
Posted by "yaooqinn (via GitHub)" <gi...@apache.org>.
yaooqinn commented on PR #45956:
URL: https://github.com/apache/spark/pull/45956#issuecomment-2046390671
cc @dongjoon-hyun @cloud-fan, PTAL when you have some time
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Re: [PR] [SPARK-47781][SQL] Handle negative scale and truncate exceed scale first for JDBC data sources [spark]
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #45956:
URL: https://github.com/apache/spark/pull/45956#discussion_r1557623773
##########
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala:
##########
@@ -196,9 +196,13 @@ object JdbcUtils extends Logging with SQLConfHelper {
case java.sql.Types.CHAR => CharType(precision)
case java.sql.Types.CLOB => StringType
case java.sql.Types.DATE => DateType
- case java.sql.Types.DECIMAL if precision != 0 || scale != 0 =>
- DecimalType.bounded(precision, scale)
- case java.sql.Types.DECIMAL => DecimalType.SYSTEM_DEFAULT
+ case java.sql.Types.DECIMAL | java.sql.Types.NUMERIC if precision != 0 || scale != 0 =>
+ if (scale < 0) {
+ DecimalPrecision.bounded(precision - scale, 0)
Review Comment:
Actually, I think these two changes are orthogonal. To support negative scale, we turn scale to 0, then it doesn't matter how we truncate the precision, as scale is already 0.
For non-negative scale, we can use a different way to truncate the precision. It's better to do it in a separate PR as it's a behavior change.
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Re: [PR] [SPARK-47781][SQL] Handle negative scale and truncate exceed scale first for JDBC data sources [spark]
Posted by "yaooqinn (via GitHub)" <gi...@apache.org>.
yaooqinn commented on PR #45956:
URL: https://github.com/apache/spark/pull/45956#issuecomment-2044649313
cc @cloud-fan
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Re: [PR] [SPARK-47781][SQL] Handle negative scale decimals for JDBC data sources [spark]
Posted by "yaooqinn (via GitHub)" <gi...@apache.org>.
yaooqinn commented on PR #45956:
URL: https://github.com/apache/spark/pull/45956#issuecomment-2046564369
+1, LGTM.
Thank you. @cloud-fan @dongjoon-hyun
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Re: [PR] [SPARK-47781][SQL] Handle negative scale and truncate exceed scale first for JDBC data sources [spark]
Posted by "yaooqinn (via GitHub)" <gi...@apache.org>.
yaooqinn commented on code in PR #45956:
URL: https://github.com/apache/spark/pull/45956#discussion_r1558703743
##########
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala:
##########
@@ -196,9 +196,13 @@ object JdbcUtils extends Logging with SQLConfHelper {
case java.sql.Types.CHAR => CharType(precision)
case java.sql.Types.CLOB => StringType
case java.sql.Types.DATE => DateType
- case java.sql.Types.DECIMAL if precision != 0 || scale != 0 =>
- DecimalType.bounded(precision, scale)
- case java.sql.Types.DECIMAL => DecimalType.SYSTEM_DEFAULT
+ case java.sql.Types.DECIMAL | java.sql.Types.NUMERIC if precision != 0 || scale != 0 =>
+ if (scale < 0) {
+ DecimalPrecision.bounded(precision - scale, 0)
Review Comment:
+1, make sense
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Re: [PR] [SPARK-47781][SQL] Handle negative scale and truncate exceed scale first for JDBC data sources [spark]
Posted by "yaooqinn (via GitHub)" <gi...@apache.org>.
yaooqinn commented on code in PR #45956:
URL: https://github.com/apache/spark/pull/45956#discussion_r1557458759
##########
connector/docker-integration-tests/src/test/scala/org/apache/spark/sql/jdbc/MySQLIntegrationSuite.scala:
##########
@@ -139,7 +139,7 @@ class MySQLIntegrationSuite extends DockerJDBCIntegrationSuite {
assert(row.getInt(3) == 77777)
assert(row.getInt(4) == 123456789)
assert(row.getLong(5) == 123456789012345L)
- val bd = new BigDecimal("123456789012345.12345678901234500000")
+ val bd = new BigDecimal("123456789012345.123456789012345000")
Review Comment:
FYI, the original value from MySQL is 123456789012345.123456789012345
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Re: [PR] [SPARK-47781][SQL] Handle negative scale decimals for JDBC data sources [spark]
Posted by "yaooqinn (via GitHub)" <gi...@apache.org>.
yaooqinn closed pull request #45956: [SPARK-47781][SQL] Handle negative scale decimals for JDBC data sources
URL: https://github.com/apache/spark/pull/45956
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