Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/15196#discussion_r80204944
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRDD.scala
---
@@ -58,11 +58,11 @@ object JDBCRDD extends Logging {
val dialect = JdbcDialects.get(url)
val conn: Connection = JdbcUtils.createConnectionFactory(url,
properties)()
try {
- val statement = conn.prepareStatement(s"SELECT * FROM $table WHERE
1=0")
+ val statement =
conn.prepareStatement(dialect.getTableExistsQuery(table))
--- End diff --
I see your point. Postgres and MySQL use `SELECT 1 FROM $table LIMIT 1`. I
suppose they could be `SELECT * ...` ? The upside is that we don't need two
separate queries. The downside is returning a row instead of 1 in these two
DB's cases?
I'll go ahead and make the change you suggest for a look.
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