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Showing entries 1 to 10 of 37 10 Older Entries

Displaying posts with tag: Stored Procedures (reset)

MariaDB 10.1 Brings Compound Statements
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A very old post of mine in 2009, MySQL’s stored procedure language could be so much more Useful suggested that it would be nice if MySQL could be adapted to use compound statements directly from the command line in a similar way to the language used for stored procedures. I’ve just seen that this seems to be possible now in MariaDB 10.1. See the release notes.

I now need to look at this. So thanks, it looks like this feature request is now available.

Capture MySQL Foreign Keys
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Shantanu asked a follow-up question on my Cleanup a MySQL Schema post from last month. He wanted to know if there was a way to capture foreign keys before removing them. The answer is yes, but how you do it depends on whether the primary key is based on a surrogate key using an auto incrementing sequence of a natural key using descriptive columns.

You can capture foreign keys with a simple query when they’re determined by a single column value. However, this script creates ALTER statements that will fail when a table holds a multiple …

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Signal from a procedure
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As I review with my students, a stored function works like a standalone program, while a stored procedure runs in the scope of another program unit. For example, you can compare the result of a function as an expression in an IF statement, like:

  IF add_numbers(1,3) > 3 THEN
    ...
  ELSE
    ...
  END IF;

You can’t call procedures inside an IF statement, but you can call the procedure and use a single OUT-mode (pass-by-reference) parameter from the procedure in a subsequent IF statement. You can implement a a wait …

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Cleanup a MySQL Schema
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My students required way to remove all their tables, views, and constraints from a MySQL database (or the alias schema). Since they’re using referential or foreign key constraints, I also wrote one procedure to drop all foreign key constraints from a database. There’s also another to drop views. The final stored procedure calls the procedure that drops foreign keys, then calls the procedure to drop views before dropping all the tables.

Here’s the dropForeignKeys stored procedure:

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SQL Injection Risks
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While I tried to deflect how you perform SQL Injection attacks against a MySQL procedure, my students requested that I post examples of what to do to avoid SQL injection, and what not to do to invite attacks. The best practice to avoid SQL injection attacks is too always bind inputs to data types, and avoid providing completely dynamic WHERE clauses.

Here’s the correct way to dynamically generate a result from a MySQL Stored Procedure:

CREATE PROCEDURE hello (IN pv_input VARCHAR(50))
BEGIN
  SELECT sample_id
  ,      sample_name
  FROM   sample
  WHERE  sample_name = pv_input;
END;
$$
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MySQL Database Triggers
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One of the students wanted an equivalent example to an Oracle DML trigger sample that replaces a white space in a last name with a dash for an INSERT statement. Apparently, the MySQL trigger example in the Oracle Database 11g and MySQL 5.6 Developer Handbook was a bit long. I have to agree with that because the MySQL DML trigger demonstrated cursors and loops in the trigger code.

Triggers can be statement- or row-level actions. Although some …

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Fun with Performance Schema
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I'm using a very small MariaDB instance as a datastore for my YouLess energy monitor, my own mail server (postfix, roundcube). It's a virtual machine from a commercial VPS provider.

All data fits in memory and the overhead of running with performance_schema on is not an issue.

While I was reading a blog post about performance_schema by Mark Leith I wanted to see what P_S could tell me about my own server.

This is the output from the first …





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PHP for MySQL Striped View
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Back in May I explained how to create MySQL striped views with session variables. A couple folks wanted to know how to implement them through PHP programs. The trick is sharing the same connection between a call to the function before a query against the striped view.

I’ve updated the MySQL example beyond the Hobbit analogy from the prior post. It now uses the following database components:

  • An APPLICATION_USER table
  • A striped AUTHORIZED_USER view
  • A FUNCTION_QUERY view to …
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Overloading Procedures
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A student asked, “Can you successfully overload MySQL stored procedures, like PL/SQL does in stored packages?” I said, “MySQL doesn’t formally support overloading stored procedures, and doesn’t support packages like Oracle 11g. You can, however, mimic (or fake) overloading with prepared statements. It requires a careful combination of stored procedures and session variables.”

Unfortunately, they asked for an example. So I wrote this set of code. It uses queries as the dynamic statements to make it simple to test but you can substitute INSERT, UPDATE, or DELETE statements. I didn’t …

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Implicit Commit Functions?
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Somebody asked about the possibility of putting DML statements inside MySQL stored functions. DML statements like the INSERT, UPDATE, and DELETE. When I said, “Yes, you can put DML statements inside functions.” They showed me the error they encountered, which is only raised at compilation when you put an explicit COMMIT statement or a Data Definition Language (DDL) statement (CREATE, ALTER, DROP, or RENAME) inside a MySQL function. The actual error message displayed is:

ERROR 1422 (HY000): Explicit OR implicit commit IS NOT allowed IN …
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Showing entries 1 to 10 of 37 10 Older Entries

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