Overview of the role of delimiter in MySQL database

The following article is mainly to describe what is the role of delimiter in MySQL database? We generally think that this command is not related to stored procedures, is this the case? The following articles will give you the relevant knowledge, hope you will have something to gain.

In fact, just tell the MySQL interpreter if the command is over and the MySQL database is ready to execute. By default, delimiter is a semicolon;. In the command-line client, if a single line of commands ends with a semicolon, the command will be executed by MySQL when the carriage returns. such as entering the following statement

1. MySQL> select * from test_table;

Then enter, then MySQL will execute the statement immediately.

But sometimes, you don't want MySQL to do this. More statements are entered for the possible, and the statement contains a semicolon. If you attempt to enter the following statement in the command line client

2. MySQL> CREATE FUNCTION ' SHORTEN ' (S VARCHAR (255), N INT)
4. MySQL> RETURNS varchar (255)
6. MySQL> BEGIN
8. MySQL> IF ISNULL (S) Then
10. MySQL> RETURN ';
12. MySQL> ELSEIF N< Then
14. MySQL> RETURN Left (S, N);
16. MySQL> ELSE
18. MySQL> IF char_length (S) <=n Then
20. MySQL> RETURN S;
22. MySQL> ELSE
24. MySQL> RETURN CONCAT (Left (s, N-10), ' ... ', right (s, 5));
26. MySQL> END IF;
28. MySQL> END IF;
30. MySQL> END;

By default, it is not possible to wait until the user has entered all of these statements before executing the entire statement. Since MySQL encounters a semicolon, it will be executed automatically. That is, the MySQL database interpreter will execute when the statement return '; In this case, the delimiter must be replaced with other symbols such as//or $$ in advance.

2. MySQL> Delimiter//
4. MySQL> CREATE FUNCTION ' SHORTEN ' (S VARCHAR (255), N INT)
6. MySQL> RETURNS varchar (255)
8. MySQL> BEGIN
10. MySQL> IF ISNULL (S) Then
12. MySQL> RETURN ';
14. MySQL> ELSEIF N< Then
16. MySQL> RETURN Left (S, N);
18. MySQL> ELSE
20. MySQL> IF char_length (S) <=n Then
22. MySQL> RETURN S;
24. MySQL> ELSE
26. MySQL> RETURN CONCAT (Left (s, N-10), ' ... ', right (s, 5));
28. MySQL> END IF;
30. MySQL> END IF;
32. MySQL> end;//

This allows the MySQL interpreter to execute this statement only when//appears

Example:

2. MySQL> Delimiter//
4. MySQL> CREATE PROCEDURE simpleproc (out param1 INT)
6. -> BEGIN
8. -> SELECT COUNT (*) into param1 from T;
10. -> END;
12. ->//
14. Query OK, 0 rows Affected (0.00 sec)
16. MySQL> delimiter;
18. MySQL> Call Simpleproc (@a);
20. Query OK, 0 rows Affected (0.00 sec)
22. MySQL> SELECT @a;
24. +------+
26. | @a |
28. +------+
30. | 3 |
32. +------+
34. 1 row in Set (0.00 sec)

The code in this article runs through MySQL 5.0.41-community-nt.

Compiled a MySQL database stored procedure for the user agent of the statistics website. This is the SQL code below.

2. drop procedure if exists pr_stat_agent;
4. --Call Pr_stat_agent (' 2008-07-17 ', ' 2008-07-18 ')
6. CREATE PROCEDURE Pr_stat_agent
8. (
10. Pi_date_from Date
12. , pi_date_to date
14. )
16. Begin
18. --Check input
20. if (Pi_date_from is null) then
22. Set Pi_date_from = current_date ();
24. End If;
26. if (pi_date_to is null) then
28. Set pi_date_to = pi_date_from;
30. End If;
32. Set pi_date_to = date_add (pi_date_from, Interval 1 day);
34. --STAT
36. Select Agent, COUNT (*) as CNT
38. From Apache_log
40. where Request_time >= pi_date_from
42. and Request_time < pi_date_to
44. Group BY Agent
46. ORDER BY CNT Desc;
48. End

I can run smoothly under EMS SQL Manager 2005 for MySQL this MySQL graphics client. But in SQLyog MySQL GUI v5.02 This client will go wrong. The last reason to find out is the problem of not setting delimiter.

By default, delimiter ";" is used to submit query statements to MySQL. There is a ";" at the end of each SQL statement in the stored procedure, and if so, it will be a problem if you submit it to MySQL every time. So change the MySQL delimiter, the above MySQL stored procedure is programmed this way:

delimiter//; --Change MySQL delimiter to: "//"

2. drop procedure if exists pr_stat_agent//
4. --Call Pr_stat_agent (' 2008-07-17 ', ' 2008-07-18 ')
6. CREATE PROCEDURE Pr_stat_agent
8. (
10. Pi_date_from Date
12. , pi_date_to date
14. )
16. Begin
18. --Check input
20. if (Pi_date_from is null) then
22. Set Pi_date_from = current_date ();
24. End If;
26. if (pi_date_to is null) then
28. Set pi_date_to = pi_date_from;
30. End If;
32. Set pi_date_to = date_add (pi_date_from, Interval 1 day);
34. --STAT
36. Select Agent, COUNT (*) as CNT
38. From Apache_log
40. where Request_time >= pi_date_from
42. and Request_time < pi_date_to
44. Group BY Agent
46. ORDER BY CNT Desc;
48. End //
50. delimiter;

Change back to the default MySQL delimiter: ";"

Of course, MySQL delimiter symbols can be set freely, you can use "/" or "$$" and so on. But the more common usage in MySQL database storage is "//" and "$$". The above-mentioned code in SQLYOG is not executed by the MySQL command line client.

Mysql> delimiter//; --Change MySQL delimiter to: "//"

2. MySQL>
4. MySQL> drop procedure if exists pr_stat_agent//
6. ->
8. ->-Call pr_stat_agent (' 2008-07-17 ', ' 2008-07-18 ')
10. ->
12. -> CREATE PROCEDURE pr_stat_agent
14. -> (
16. -> Pi_date_from date
18. ->, pi_date_to date
20. ->)
22. -> Begin
24. ->--Check input
26. -> if (pi_date_from is null) then
28. -> Set pi_date_from = current_date ();
30. -> End If;
32. ->
34. -> if (pi_date_to is null) then
36. -> Set pi_date_to = pi_date_from;
38. -> End If;
40. ->
42. -> Set pi_date_to = date_add (pi_date_from, Interval 1 day);
44. ->
46. ->-STAT
48. -> select agent, Count (*) as CNT
50. -> from Apache_log
52. -> where request_time >= pi_date_from
54. -> and Request_time < pi_date_to
56. -> Group by Agent
58. -> ORDER BY cnt DESC;
60. -> end;//
62. ->
64. -> delimiter;

Change back to the default MySQL delimiter: ";"

1. ->//
2. ->//
3. ->//
4. ->;
5. ->;
6. ->

It's strange! Finally found the problem, the MySQL command line run "delimiter//;" Then the MySQL delimiter is actually "//;" Instead of "//" as we expected. In fact, just run the command "delimiter//" is OK.

Mysql> delimiter//--no sign at the end ";"

2. MySQL>
4. MySQL> drop procedure if exists pr_stat_agent//
6. Query OK, 0 rows Affected (0.00 sec)
8. MySQL>
10. MySQL>--Call Pr_stat_agent (' 2008-07-17 ', ' 2008-07-18 ')
12. MySQL>
14. MySQL> CREATE PROCEDURE pr_stat_agent
16. -> (
18. -> Pi_date_from date
20. ->, pi_date_to date
22. ->)
24. -> Begin
26. ->--Check input
28. -> if (pi_date_from is null) then
30. -> Set pi_date_from = current_date ();
32. -> End If;
34. ->
36. -> if (pi_date_to is null) then
38. -> Set pi_date_to = pi_date_from;
40. -> End If;
42. ->
44. -> Set pi_date_to = date_add (pi_date_from, Interval 1 day);
46. ->
48. ->-STAT
50. -> select agent, Count (*) as CNT
52. -> from Apache_log
54. -> where request_time >= pi_date_from
56. -> and Request_time < pi_date_to
58. -> Group by Agent
60. -> ORDER BY cnt DESC;
62. -> end;//
64. Query OK, 0 rows Affected (0.00 sec)
66. MySQL>
68. MySQL> delimiter;

Do not sign "//" at the end

1. MySQL>

Incidentally, we can execute the SQL code in the file in the MySQL database. For example, I put the code for the stored procedure above in the file D:\pr_stat_agent.sql. You can run the following code to establish a stored procedure.

1. MySQL> Source D:\pr_stat_agent.sql
2. Query OK, 0 rows Affected (0.00 sec)
3. Query OK, 0 rows Affected (0.00 sec)

The abbreviated form of the source directive is: "\."

1. MySQL> \. d:\pr_stat_agent.sql
2. Query OK, 0 rows Affected (0.00 sec)
3. Query OK, 0 rows Affected (0.00 sec)

Finally, the client tools for the MySQL database are visible in some places, each with its own set.

Overview of the role of delimiter in MySQL database