116.Oracle数据库SQL开发之 PLSQL编程——游标
116.Oracle数据库SQL开发之 PLSQL编程——游标
欢迎转载，转载请标明出处：http://blog.csdn.net/notbaron/article/details/50086931
可以使用游标获取查询返回的记录。在通过查询将记录检索到游标中后，可以一次从游标中取出一行。使用游标时一般需要遵循以下5个步骤：
1. 声明一些变量，用于保存记录的列值
2. 声明游标，并指定查询
3. 打开游标
4. 一次从游标中获得一个记录，并将列值存储在第一步声明的变量中，然后对这些变量执行某些操作
5. 关闭游标
1. 步骤1：声明用于保存列值的变量
声明用于保存列值的变量。变量必须与列的类型兼容。
例如：
DECLARE
V_product_idproducts.product_id%TYPE;
V_name products.name%TYPE;
V_price products.price%TYPE;
2. 步骤2：声明游标
游标的声明由游标名和希望执行的查询组成。游标声明与其他的声明一样。
声明游标的语法如下：
CURSOR cursor_name IS
SELECT_statement;
查询在开发游标之前不会真正运行。
3. 步骤3：打开游标
打开游标时使用的是OPEN语句，这个语句必须放置在代码块的可执行段中。
例如：
OPEN v_product_cursor;
4. 步骤4：从游标中取得记录
从游标中取得每一条记录，可使用FETCH语句。FETCH语句将列的值读取到的第一步中声明的变量中：语法如下：
FETCH cursor_name
INTOvariable[,variable … ];
游标可能包含多条记录；因此要通过循环依次读取每一条记录。为了确定循环是否结束，可以使用布尔变量v_product_cursor%NOTFOUND。
5. 步骤5：关闭游标
使用CLOSE语句关闭游标。关闭游标可释放系统资源。
例如：
CLOSE v_product_cursor;
6. 示例
如下：
SET SERVEROUTPUT ON
DECLARE
-- step 1:declare the variables
v_product_idproducts.product_id%TYPE;
v_name products.name%TYPE;
v_price products.price%TYPE;
-- step 2:declare the cursor
CURSORv_product_cursor IS
SELECTproduct_id, name, price
FROMproducts
ORDER BYproduct_id;
BEGIN
-- step 3:open the cursor
OPENv_product_cursor;
LOOP
-- step 4:fetch the rows from the cursor
FETCHv_product_cursor
INTOv_product_id, v_name, v_price;
-- exit theloop when there are no more rows, as indicated by
-- theBoolean variable v_product_cursor%NOTFOUND (= true when
-- thereare no more rows)
EXIT WHENv_product_cursor%NOTFOUND;
-- useDBMS_OUTPUT.PUT_LINE() to display the variables
DBMS_OUTPUT.PUT_LINE(
'v_product_id = ' || v_product_id || ', v_name = ' || v_name ||
',v_price = ' || v_price
);
END LOOP;
-- step 5:close the cursor
CLOSEv_product_cursor;
END;
/
运行如下：
SQL>@product_cursor.sql
输出如下：
store@PDB1> @product_cursor.sql
v_product_id = 1, v_name = Modern Science,v_price = 40
v_product_id = 2, v_name = New Chemistry,v_price = 35
v_product_id = 3, v_name = Supernova,v_price = 25.99
v_product_id = 4, v_name = Tank War,v_price = 13.95
v_product_id = 5, v_name = Z Files, v_price= 49.99
v_product_id = 6, v_name = 2412: TheReturn, v_price = 14.95
v_product_id = 7, v_name = Space Force 9,v_price = 13.49
v_product_id = 8, v_name = From AnotherPlanet, v_price = 12.99
v_product_id = 9, v_name = Classical Music,v_price = 10.99
v_product_id = 10, v_name = Pop 3, v_price= 15.99
v_product_id = 11, v_name = Creative Yell,v_price = 14.99
v_product_id = 12, v_name = My Front Line,v_price = 13.49
v_product_id = 13, v_name = Lunar Landing,v_price = 15.99
v_product_id = 14, v_name = Submarine,v_price = 15.99
v_product_id = 15, v_name = Airplane,v_price = 15.99
PL/SQL procedure successfully completed.
7. 游标与FOR 循环
利用FOR循环可以访问游标中的记录。当使用FOR循环时，可以不显示地打开和关闭游标——for循环会自动执行这些操作。
例如：
SET SERVEROUTPUTON
DECLARE
CURSOR v_product_cursor IS
SELECT product_id, name, price
FROM products
ORDER BY product_id;
BEGIN
FOR v_product IN v_product_cursor LOOP
DBMS_OUTPUT.PUT_LINE(
'product_id = ' || v_product.product_id||
', name = ' || v_product.name ||
', price = ' || v_product.price
);
END LOOP;
END;
/
输出如下：
store@PDB1> @product_cursor2.sql
product_id = 1, name = Modern Science,price = 40
product_id = 2, name = New Chemistry, price= 35
product_id = 3, name = Supernova, price =25.99
product_id = 4, name = Tank War, price =13.95
product_id = 5, name = Z Files, price =49.99
product_id = 6, name = 2412: The Return,price = 14.95
product_id = 7, name = Space Force 9, price= 13.49
product_id = 8, name = From Another Planet,price = 12.99
product_id = 9, name = Classical Music,price = 10.99
product_id = 10, name = Pop 3, price =15.99
product_id = 11, name = Creative Yell,price = 14.99
product_id = 12, name = My Front Line,price = 13.49
product_id = 13, name = Lunar Landing,price = 15.99
product_id = 14, name = Submarine, price =15.99
product_id = 15, name = Airplane, price =15.99
PL/SQL procedure successfully completed.
8. OPEN-FOR语句
可以对游标使用OPEN-FOR语句，由于可以将游标分配给不同的查询，因此可以更加灵活地处理游标。如下：
SET SERVEROUTPUT ON
DECLARE
-- declare aREF CURSOR type named t_product_cursor
TYPEt_product_cursor IS
REF CURSORRETURN products%ROWTYPE;
-- declare at_product_cursor object named v_product_cursor
v_product_cursor t_product_cursor;
-- declare anobject to store columns from the products table
-- namedv_product (of type products%ROWTYPE)
v_productproducts%ROWTYPE;
BEGIN
-- assign aquery to v_product_cursor and open it using OPEN-FOR
OPENv_product_cursor FOR
SELECT * FROMproducts WHERE product_id < 5;
-- use a loopto fetch the rows from v_product_cursor into v_product
LOOP
FETCHv_product_cursor INTO v_product;
EXIT WHENv_product_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(
'product_id = ' || v_product.product_id ||
', name = ' || v_product.name ||
', price= ' || v_product.price
);
END LOOP;
-- closev_product_cursor
CLOSEv_product_cursor;
END;
/
在DECLARE代码块中，下面的语句声明了一个REF CURSOR类型，并命名为t_product_cursor。
REF CURSOR是一个指向游标的指针，类似于C++编程语言中的指针。
执行如下：
store@PDB1> @product_cursor3.sql
product_id = 1, name = Modern Science,price = 40
product_id = 2, name = New Chemistry, price= 35
product_id = 3, name = Supernova, price =25.99
product_id = 4, name = Tank War, price =13.95
PL/SQL procedure successfully completed.
9. 无约束游标
有具体的返回类型，这些游标称为约束游标。约束游标的返回类型必须与游标运行的查询中的列相匹配。无约束游标没有返回类型，因此可以运行任何查询。
如下：
SET SERVEROUTPUT ON
DECLARE
TYPE t_cursorIS REF CURSOR;
v_cursort_cursor;
v_productproducts%ROWTYPE;
v_customercustomers%ROWTYPE;
BEGIN
OPEN v_cursorFOR
SELECT * FROMproducts WHERE product_id < 5;
LOOP
FETCHv_cursor INTO v_product;
EXIT WHENv_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(
'product_id = ' || v_product.product_id ||
', name =' || v_product.name ||
', price= ' || v_product.price
);
END LOOP;
OPEN v_cursorFOR
SELECT * FROMcustomers WHERE customer_id < 3;
LOOP
FETCHv_cursor INTO v_customer;
EXIT WHENv_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE(
'customer_id = ' || v_customer.customer_id ||
',first_name = ' || v_customer.first_name ||
',last_name = ' || v_customer.last_name
);
END LOOP;
CLOSEv_cursor;
END;
/
执行如下：
store@PDB1> @unconstrained_cursor.sql
product_id = 1, name = Modern Science,price = 40
product_id = 2, name = New Chemistry, price= 35
product_id = 3, name = Supernova, price =25.99
product_id = 4, name = Tank War, price =13.95
customer_id = 1, first_name = John,last_name = Brown
customer_id = 2, first_name = Cynthia,last_name = Green
PL/SQL procedure successfully completed.