MAPREDUCE-1224. Calling "SELECT t.* from <table> AS t" to get meta information is too expensive for big tables. Contributed by Spencer Ho.

From: Thomas White <tomwhite@apache.org>

git-svn-id: https://svn.apache.org/repos/asf/incubator/sqoop/trunk@1149844 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/hadoop/sqoop/manager/SqlManager.java

@@ -67,7 +67,8 @@ public SqlManager(final SqoopOptions opts) {
    * be tuned per-database, but the main extraction loop is still inheritable.
    */
   protected String getColNamesQuery(String tableName) {
-    return "SELECT t.* FROM " + tableName + " AS t";
+    // adding where clause to prevent loading a big table
+    return "SELECT t.* FROM " + tableName + " AS t WHERE 1=0";
   }
 
   @Override