IDENTIFIER 子句
說明
將常數 STRING 表達式轉換為 SQL 物件名稱。此子句的目的是允許在 SQL 陳述式中建立識別碼範本，而不會增加 SQL 注入攻擊的風險。通常，此子句會與參數標記一起用作引數。
語法
IDENTIFIER ( strExpr )
參數
- strExpr：常數
STRING表達式。通常，表達式會包含參數標記。
傳回
可作為下列項目的（合格）識別碼
- 合格的資料表名稱
- 命名空間名稱
- 函數名稱
- 合格的欄或屬性參考
範例
這些範例使用已命名的參數標記建立查詢範本。
// Creation of a table using parameter marker.
spark.sql("CREATE TABLE IDENTIFIER(:mytab)(c1 INT)", args = Map("mytab" -> "tab1")).show()
spark.sql("DESCRIBE IDENTIFIER(:mytab)", args = Map("mytab" -> "tab1")).show()
+--------+---------+-------+
|col_name|data_type|comment|
+--------+---------+-------+
| c1| int| NULL|
+--------+---------+-------+
// Altering a table with a fixed schema and a parameterized table name.
spark.sql("ALTER TABLE IDENTIFIER('default.' || :mytab) ADD COLUMN c2 INT", args = Map("mytab" -> "tab1")).show()
spark.sql("DESCRIBE IDENTIFIER(:mytab)", args = Map("mytab" -> "default.tab1")).show()
+--------+---------+-------+
|col_name|data_type|comment|
+--------+---------+-------+
| c1| int| NULL|
| c2| int| NULL|
+--------+---------+-------+
// A parameterized reference to a table in a query. This table name is qualified and uses back-ticks.
spark.sql("SELECT * FROM IDENTIFIER(:mytab)", args = Map("mytab" -> "`default`.`tab1`")).show()
+---+---+
| c1| c2|
+---+---+
+---+---+
// You cannot qualify the IDENTIFIER clause or use it as a qualifier itself.
spark.sql("SELECT * FROM myschema.IDENTIFIER(:mytab)", args = Map("mytab" -> "`tab1`")).show()
[INVALID_SQL_SYNTAX.INVALID_TABLE_VALUED_FUNC_NAME] `myschema`.`IDENTIFIER`.
spark.sql("SELECT * FROM IDENTIFIER(:myschema).mytab", args = Map("mychema" -> "`default`")).show()
[PARSE_SYNTAX_ERROR]
// Dropping a table with separate schema and table parameters.
spark.sql("DROP TABLE IDENTIFIER(:myschema || '.' || :mytab)", args = Map("myschema" -> "default", "mytab" -> "tab1")).show()
// A parameterized column reference
spark.sql("SELECT IDENTIFIER(:col) FROM VALUES(1) AS T(c1)", args = Map("col" -> "t.c1")).show()
+---+
| c1|
+---+
| 1|
+---+
// Passing in a function name as a parameter
spark.sql("SELECT IDENTIFIER(:func)(-1)", args = Map("func" -> "abs")).show();
+-------+
|abs(-1)|
+-------+
| 1|
+-------+