oracle stored procedure sql statement

Oracle database is an efficient database management system with rich functions and extremely high reliability, and is widely used in enterprise-level applications. Oracle stored procedures are a special program unit that can combine and store multiple SQL statements and are used in daily data processing tasks. This article will introduce how to write SQL statements in Oracle stored procedures.

1. Why use stored procedures

When developing enterprise applications, we usually encounter a variety of data processing tasks, such as data import, data cleaning, data conversion, data Analysis etc. Among these tasks, SQL statements are the most important tools and can perform various processing operations on data. However, for complex data processing tasks, multiple SQL statements may need to be written, and these SQL statements may be used repeatedly. If you write SQL statements manually every time, it is not only time-consuming and labor-intensive, but also errors may occur. At this time, stored procedures can come into play.

A stored procedure is a special program unit that can group multiple SQL statements together to form an overall logical unit. Stored procedures can encapsulate and reuse SQL statements, thereby simplifying code writing and maintenance and improving development efficiency. In addition, stored procedures can also improve database performance and reduce the number of interactions with the database, thereby reducing network latency and data transmission losses.

2. Basic syntax of stored procedures

Stored procedures are written in PL/SQL language. PL/SQL is a programming language dedicated to Oracle database and supports object-oriented programming and procedural programming. A stored procedure consists of three parts: declaration part, procedure body part and exception handling part.

1. Declaration Section

DECLARE

（变量声明部分）

BEGIN

（过程体部分）

EXCEPTION

（异常处理部分）

END;

Among them, "DECLARE" represents the declaration part, "BEGIN" represents the process body part, and "EXCEPTION" represents the exception handling part. In the declaration part, you need to declare the variables, cursors and other data structures required by the process so that these data structures can be used in the process body.

2. Process body part

In the process body part, specific SQL statements and PL/SQL code will be written, and the variables and variables declared in the declaration part can be used Cursor and other data structures. In the process body, you can use SQL statements to access data structures such as tables and views in the database, and you can use cursor objects to store query result sets. At the same time, control flow structures can also be used in the process body to implement operations such as loops and branches. For example:

BEGIN

--声明变量
DECLARE
     var1 VARCHAR2(20);
BEGIN
     --执行sql语句并存储结果
     SELECT column1 INTO var1
     FROM table1
     WHERE id=1;
     --输出结果
     dbms_output.put_line(var1);
END;

END;

In the above code, we declared a variable named var1 in the declaration section and used SELECT in the procedure body statement to query the data with id 1 in table1, assign the query result to variable var1, and finally output the result. In the process body, dbms_output.put_line() is also called to output the results.

3. Exception handling part

The exception handling part is used to handle exceptions that may occur during execution. In the exception handling section, the "EXCEPTION" keyword is usually used to define the exception type, and the "WHEN" keyword is used to specifically specify the exception type and corresponding processing operation. For example:

BEGIN

--声明变量
DECLARE
     var1 VARCHAR2(20);
BEGIN
     --执行sql语句并存储结果
     SELECT column1 INTO var1
     FROM table1
     WHERE id=1;
     --输出结果
     dbms_output.put_line(var1);
EXCEPTION
     WHEN no_data_found THEN
          dbms_output.put_line('查询结果为空');
     WHEN others THEN
          dbms_output.put_line('发生未知异常');
END;

END;

In the above code, when the SELECT statement does not find any results, the no_data_found exception will be triggered and "The query result is empty" will be output. " prompt message; when other unknown exceptions occur, the others exception will be triggered, and the prompt message "Unknown exception occurred" will be output.

3. Example application of stored procedures

The following is a practical example showing how to use stored procedures to handle data processing tasks in enterprise applications:

DECLARE

--声明变量和游标对象
v_empno NUMBER; --员工编号
v_ename VARCHAR2(20); --员工姓名
v_sal NUMBER; --员工工资
v_count NUMBER := 0; --统计变量
CURSOR c_emp IS SELECT * FROM emp;

BEGIN

FOR emp_rec IN c_emp LOOP
     v_empno := emp_rec.empno;
     v_ename := emp_rec.ename;
     v_sal   := emp_rec.sal;

     --如果工资低于2000，将工资增加1000
     IF v_sal<2000 THEN
          UPDATE emp SET sal=sal+1000 WHERE empno=v_empno;
          v_count := v_count + 1;
     END IF;
END LOOP;

--输出处理结果
dbms_output.put_line('共更新了'||v_count||'行数据');

EXCEPTION

WHEN others THEN
     dbms_output.put_line('发生异常：'||SQLERRM);

END;

In the above code, we first declare several variables and a cursor object, which are used in the procedure body The FOR loop traverses all records in the emp table. For each record, determine whether the employee's salary is less than 2,000. If so, increase his salary by 1,000, and finally return the number of successfully updated rows. In the exception handling section, handle exception situations that may arise. This example simply shows how to use stored procedures to write SQL statements to process data. In actual applications, more complex operations can be performed according to requirements.

Summary:

This article briefly introduces the concept and basic syntax of Oracle stored procedures, especially how to write SQL statements to implement data processing tasks. Stored procedures can encapsulate and reuse SQL statements, thereby simplifying code writing and maintenance and improving development efficiency. In addition, stored procedures can also improve database performance and reduce the number of interactions with the database, thereby reducing network latency and data transmission losses. In actual development, we need to write stored procedures according to actual needs and pay attention to the handling of exceptions. Using stored procedures to write SQL statements is a recommended practice for both beginners and experienced developers.

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