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Author: asfernandes

doc/sql.extensions/README.create_table_as_query.md

@@ -16,8 +16,8 @@ the same number of columns as the query result.
 If no column name list is specified, column names are taken from the query output names. Unnamed expressions must
 be explicitly aliased.
 
-`WITH DATA` is the default and inserts the query result into the newly created table. `WITH NO DATA` creates only
-the table definition.
+`WITH DATA` is the default and inserts the query result into the newly created table in the same transaction.
+`WITH NO DATA` creates only the table definition.
 
 For global and local temporary tables, normal temporary-table data lifetime rules apply. Package temporary tables
 do not support this syntax.
@@ -53,3 +53,56 @@ CREATE LOCAL TEMPORARY TABLE tx_work AS
     FROM employee
   WITH NO DATA;
 ```
+
+## ISQL behavior
+
+ISQL in AUTODDL mode (the default) uses separate transactions for DDL and DML statements.
+When `CREATE TABLE ... AS <query>` is executed with `WITH DATA`, the table creation and data population occur in the
+DDL transaction.
+
+For regular tables, the inserted rows are not visible to the DML transaction until the DDL transaction is committed.
+For temporary tables, this behavior is even more surprising because the rows belong to the DDL transaction and are
+therefore not visible to the DML transaction at all.
+
+For example:
+
+```sql
+SQL> CREATE TABLE T1 AS SELECT 1 A FROM RDB$DATABASE;
+SQL> SELECT * FROM T1;
+
+SQL> COMMIT;
+SQL> SELECT * FROM T1;
+
+           A
+============
+           1
+```
+
+With a temporary table:
+
+```sql
+SQL> CREATE GLOBAL TEMPORARY TABLE T1 AS SELECT 1 A FROM RDB$DATABASE;
+SQL> SELECT * FROM T1;
+
+SQL> COMMIT;
+SQL> SELECT * FROM T1;
+```
+
+The table exists, but no rows are returned because the data was inserted in the DDL transaction and is not visible to
+the DML transaction.
+
+To avoid this behavior, disable AUTODDL before executing the statement:
+
+```sql
+SQL> SET AUTODDL OFF;
+
+SQL> CREATE GLOBAL TEMPORARY TABLE T1 AS SELECT 1 A FROM RDB$DATABASE;
+SQL> SELECT * FROM T1;
+
+           A
+============
+           1
+```
+
+When AUTODDL is disabled, both the table creation and data population occur in the current transaction, making the
+inserted rows immediately visible.