Github user danielvdende commented on a diff in the pull request:
https://github.com/apache/spark/pull/20057#discussion_r168943159
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala ---
@@ -85,15 +85,24 @@ private object PostgresDialect extends JdbcDialect {
s"SELECT 1 FROM $table LIMIT 1"
}
+ override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
+
/**
- * The SQL query used to truncate a table. For Postgres, the default
behaviour is to
- * also truncate any descendant tables. As this is a (possibly unwanted)
side-effect,
- * the Postgres dialect adds 'ONLY' to truncate only the table in question
- * @param table The name of the table.
- * @return The SQL query to use for truncating a table
- */
- override def getTruncateQuery(table: String): String = {
- s"TRUNCATE TABLE ONLY $table"
+ * The SQL query used to truncate a table. For Postgres, the default
behaviour is to
+ * also truncate any descendant tables. As this is a (possibly unwanted)
side-effect,
+ * the Postgres dialect adds 'ONLY' to truncate only the table in
question
+ * @param table The table to truncate
+ * @param cascade Whether or not to cascade the truncation. Default
value is the value of
+ * isCascadingTruncateTable()
+ * @return The SQL query to use for truncating a table
+ */
+ override def getTruncateQuery(
+ table: String,
+ cascade: Option[Boolean] = isCascadingTruncateTable): String = {
+ cascade match {
+ case Some(true) => s"TRUNCATE TABLE ONLY $table CASCADE"
--- End diff --
Sure, I made a quick example, as you can see using `TRUNCATE TABLE ONLY
$table CASCADE` will truncate the foreign key-ed table, but leave the
inheritance relationship intact:
```postgres=# CREATE SCHEMA test;
CREATE SCHEMA
postgres=# CREATE TABLE parent(a INT);
CREATE TABLE
postgres=# ALTER TABLE parent ADD CONSTRAINT some_constraint PRIMARY KEY(a);
ALTER TABLE
postgres=# CREATE TABLE child(b INT) INHERITS (parent);
CREATE TABLE
postgres=# CREATE TABLE forkey(c INT);
CREATE TABLE
postgres=# ALTER TABLE forkey ADD FOREIGN KEY(c) REFERENCES parent(a);
ALTER TABLE
postgres=# INSERT INTO parent VALUES(1);
INSERT 0 1
postgres=# select * from parent;
a
---
1
(1 row)
postgres=# select * from child;
a | b
---+---
(0 rows)
postgres=# INSERT INTO child VALUES(2);
INSERT 0 1
postgres=# select * from child;
a | b
---+---
2 |
(1 row)
postgres=# select * from parent;
a
---
1
2
(2 rows)
postgres=# INSERT INTO forkey VALUES(1);
INSERT 0 1
postgres=# select * from forkey;
c
---
1
(1 row)
postgres=# TRUNCATE TABLE ONLY parent CASCADE;
NOTICE: truncate cascades to table "forkey"
TRUNCATE TABLE
postgres=# select * from parent;
a
---
2
(1 row)
postgres=# select * from child;
a | b
---+---
2 |
(1 row)
postgres=# select * from forkey;
c
---
(0 rows)
```
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