Oracle 11G 虚拟列 Virtual Column 介绍
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Oracle 11G 虚拟列 Virtual Column Oracle 11G 在表中引入了虚拟列，虚拟列是一个表达式，在运行时计算，不存储在数据库中，不能更新虚拟列的值。 定义一个虚拟列的语法： column_name [datatype] [GENERATED ALWAYS] AS [expression] [VIRTUAL] 1.虚拟列可以用在select，update，delete语句的where条件中，但是不能用于DML语句 2.可以基于虚拟列来做分区 3. 可以在虚拟列上建索引，oracle的函数索引就类似。 4. 可以在虚拟列上建约束 创建一个带虚拟列的表： CREATE TABLE EMPLOYEE ( empl_id NUMBER, empl_nm VARCHAR2(50), monthly_sal NUMBER(10,2), bonus NUMBER(10,2), total_sal NUMBER(10,2) GENERATED ALWAYS AS (monthly_sal*12 + bonus) ); total_sal就是一个虚拟列 查看下表定义内容： SELECT column_name, data_type, data_length, data_default, virtual_column FROM user_tab_cols WHERE table_name = 'EMPLOYEE'; COLUMN_NAME | DATA_TYPE | DATA_LENGTH | DATA_DEFAULT | VIRTUAL_COLUMN EMPL_ID | NUMBER | 22 | null | NO EMPL_NM | VARCHAR2 | 50 | null | NO MONTHLY_SAL | NUMBER | 22 | null | NO BONUS | NUMBER | 22 | null | NO TOTAL_SAL | NUMBER | 22 | "MONTHLY_SAL"*12+"BONUS" | YES virtual_column是yes，表示是虚拟列，我们也可以在建表语句加上VIRTUAL，显示声明为虚拟列 DROP TABLE EMPLOYEE PURGE; CREATE OR REPLACE FUNCTION get_empl_total_sal ( p_monthly_sal NUMBER, p_bonus NUMBER) RETURN NUMBER DETERMINISTIC IS BEGIN RETURN p_monthly_sal * 12 + p_bonus; END; CREATE TABLE EMPLOYEE (empl_id NUMBER, empl_nm VARCHAR2(50), monthly_sal NUMBER(10,2), bonus NUMBER(10,2), total_sal NUMBER(10,2) AS (get_empl_total_sal(monthly_sal, bonus)) VIRTUAL ); 我们可以在虚拟列上创建索引 CREATE INDEX idx_total_sal ON employee(total_sal); SELECT index_name, index_type FROM user_indexes WHERE table_name = 'EMPLOYEE'; INDEX_NAME INDEX_TYPE IDX_TOTAL_SAL FUNCTION-BASED NORMAL 这个函数也是表定义内容 DROP FUNCTION get_empl_total_sal; SELECT * FROM employee; * Error at line 0 ORA-00904: "schema"."GET_EMPL_TOTAL_SAL": invalid identifier 可以添加一个虚拟列 DROP TABLE EMPLOYEE PURGE; CREATE TABLE EMPLOYEE (empl_id NUMBER, empl_nm VARCHAR2(50), monthly_sal NUMBER(10,2), bonus NUMBER(10,2) ); ALTER TABLE EMPLOYEE ADD (total_sal AS (monthly_sal * 12 + bonus)); 这个新列的类型时不确定的，是根据表达式来推断的。 INSERT INTO employee (empl_id, empl_nm, monthly_sal, bonus) WITH DATA AS (SELECT 100 empl_id, 'AAA' empl_nm, 20000 monthly_sal, 3000 bonus FROM DUAL UNION SELECT 200, 'BBB', 12000, 2000 FROM DUAL UNION SELECT 300, 'CCC', 32100, 1000 FROM DUAL UNION SELECT 400, 'DDD', 24300, 5000 FROM DUAL UNION SELECT 500, 'EEE', 12300, 8000 FROM DUAL) SELECT * FROM DATA; SELECT * FROM employee; EMPL_ID | EMPL_NM | MONTHLY_SAL | BONUS | TOTAL_SAL 100 | AAA | 20000 | 3000 | 243000 200 | BBB | 12000 | 2000 | 146000 300 | CCC | 32100 | 1000 | 386200 400 | DDD | 24300 | 5000 | 296600 500 | EEE | 12300 | 8000 | 155600 在虚拟列上执行update语句是不允许的 UPDATE employee SET total_sal = 2000; ORA-54017: UPDATE operation disallowed on virtual columns 能够从虚拟列上收集表的统计信息 EXEC DBMS_STATS.GATHER_TABLE_STATS(user, 'EMPLOYEE'); SELECT column_name, num_distinct, display_raw (low_value, data_type) low_value, display_raw (high_value, data_type) high_value FROM dba_tab_cols WHERE table_name = 'EMPLOYEE'; COLUMN_NAME | NUM_DISTINCT | LOW_VALUE | HIGH_VALUE TOTAL_SAL | 5 | 146000 | 386200 BONUS | 5 | 1000 | 8000 MONTHLY_SAL | 5 | 12000 | 32100 EMPL_NM | 5 | AAA | EEE EMPL_ID | 5 | 100 | 500 基于虚拟列的分区 DROP TABLE EMPLOYEE PURGE; CREATE TABLE employee (empl_id NUMBER, empl_nm VARCHAR2(50), monthly_sal NUMBER(10,2), bonus NUMBER(10,2), total_sal NUMBER(10,2) AS (monthly_sal*12 + bonus) ) PARTITION BY RANGE (total_sal) (PARTITION sal_200000 VALUES LESS THAN (200000), PARTITION sal_400000 VALUES LESS THAN (400000), PARTITION sal_600000 VALUES LESS THAN (600000), PARTITION sal_800000 VALUES LESS THAN (800000), PARTITION sal_default VALUES LESS THAN (MAXVALUE)); INSERT INTO employee (empl_id, empl_nm, monthly_sal, bonus) WITH DATA AS (SELECT 100 empl_id, 'AAA' empl_nm, 20000 monthly_sal, 3000 bonus FROM DUAL UNION SELECT 200, 'BBB', 12000, 2000 FROM DUAL UNION SELECT 300, 'CCC', 32100, 1000 FROM DUAL UNION SELECT 400, 'DDD', 24300, 5000 FROM DUAL UNION SELECT 500, 'EEE', 12300, 8000 FROM DUAL) SELECT * FROM DATA; EXEC DBMS_STATS.GATHER_TABLE_STATS(user,'EMPLOYEE',granularity => 'PARTITION'); SELECT table_name, partition_name, num_rows FROM user_tab_partitions WHERE table_name = 'EMPLOYEE' ORDER BY partition_name; TABLE_NAME | PARTITION_NAME | NUM_ROWS EMPLOYEE | SAL_200000 | 2 EMPLOYEE | SAL_400000 | 3 EMPLOYEE | SAL_600000 | 0 EMPLOYEE | SAL_800000 | 0 EMPLOYEE | SAL_DEFAULT | 0 在分区情况下，不能更新虚拟列引用的列 UPDATE employee SET monthly_sal = 30000 WHERE empl_id = 500; ORA-14402: updating partition key column would cause a partition change 如果在分区情况能够更新，则需要设置ENABLE ROW MOVEMENT ALTER TABLE employee ENABLE ROW MOVEMENT; UPDATE employee SET monthly_sal = 80000 WHERE empl_id = 500; 1 row updated. 不能基于函数表达式的虚拟列上的分区 CREATE TABLE employee_new (empl_id NUMBER, empl_nm VARCHAR2(50), monthly_sal NUMBER(10,2), bonus NUMBER(10,2), total_sal NUMBER(10,2) AS (get_empl_total_sal(monthly_sal, bonus)) ) PARTITION BY RANGE (total_sal) (PARTITION sal_200000 VALUES LESS THAN (200000), PARTITION sal_400000 VALUES LESS THAN (400000), PARTITION sal_600000 VALUES LESS THAN (600000), PARTITION sal_800000 VALUES LESS THAN (800000), PARTITION sal_default VALUES LESS THAN (MAXVALUE)); ORA-54021: Cannot use PL/SQL expressions in partitioning or subpartitioning columns
