errmsg("cannot alter system column \"%s\"",

colName)));

/*

* Cannot specify USING when altering type of a generated column, because

* that would violate the generation expression.

*/

if (attTup->attgenerated && def->cooked_default)

ereport(ERROR,

(errcode(ERRCODE_INVALID_COLUMN_DEFINITION),

errmsg("cannot specify USING when altering type of generated column"),

errdetail("Column \"%s\" is a generated column.", colName)));

/*

* Don't alter inherited columns. At outer level, there had better not be

* any inherited definition; when recursing, we assume this was checked at

(errcode(ERRCODE_DATATYPE_MISMATCH),

errmsg("column \"%s\" cannot be cast automatically to type %s",

colName, format_type_be(targettype)),

!attTup->attgenerated ?

/* translator: USING is SQL, don't translate it */

errhint("You might need to specify \"USING %s::%s\".",

quote_identifier(colName),

format_type_with_typemod(targettype,

targettypmod))));

targettypmod)) : 0));

}

/* Fix collations after all else */

(2 rows)

ALTER TABLE gtest27 ALTER COLUMN x TYPE boolean USING x <> 0; -- error

ERROR: generation expression for column "x" cannot be cast automatically to type boolean

ERROR: cannot specify USING when altering type of generated column

DETAIL: Column "x" is a generated column.

ALTER TABLE gtest27 ALTER COLUMN x DROP DEFAULT; -- error

ERROR: column "x" of relation "gtest27" is a generated column

HINT: Use ALTER TABLE ... ALTER COLUMN ... DROP EXPRESSION instead.