Showing entries 1 to 7
Displaying posts with tag: SQL/PSM (reset)
MySQL Shell Parsing

I’ve been experimenting with the mysqlsh since installing it last week. It’s been interesting. Overall, I’m totally impressed but I did find a problem with how it parses stored procedures.

First thought is always, is it my code? I checked the file by running it as a script file through MySQL Workbench. It ran perfectly in MySQL Workbench but failed repeatedly when run from the mysqlsh utility. Next step, reduce the code to a small test case, retest it, and log a bug if it is replicated. My test case in a test.sql file generates the following errors when run from the mysqlsh utility:

 MySQL  localhost:33060+ ssl  studentdb  SQL > source test.sql
Query OK, 0 rows affected (0.0003 sec)
ERROR: 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the …
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Capture MySQL Foreign Keys

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 column foreign key value. The SELECT statement would look like this when capturing all foreign key values in a MySQL Server:

      SELECT   CONCAT('ALTER TABLE',' ',tc.table_schema,'.',tc.table_name,' '
               ,'ADD CONSTRAINT',' …
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SQL Injection Risks

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))
  SELECT sample_id
  ,      sample_name
  FROM   sample
  WHERE  sample_name = pv_input;

A call to this hello procedure will only return the row or rows where the pv_input value matches the sample_name column value. Any attempt to exploit it like the one below fails.

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MySQL Database Triggers

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 databases let you define statement-level triggers, MySQL doesn’t support them. MySQL only supports row-level triggers. Row-level triggers support critical or non-critical behaviors. Critical behavior means the trigger observes an insert, update, or delete that must be stopped, which means it …

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Placement over substance

I was stunned when a SQL query raised an ERROR 1630 (42000) telling me the SUM function didn’t exist in MySQL 5.5.23. The fix was simple. The opening parenthesis of the SUM function must be on the same line as the SUM keyword without an intervening white space. Alternatively phrased, you can’t have a line return or white space between the SUM function name and the opening parenthesis of the call parameter list. The same rule doesn’t apply to the opening parenthesis of the FORMAT function and it seems to me that this parsing inconsistency is problematic.

Therefore, my surprise, observation, and complaint is that all functions don’t parse the same way, using the same rules. That is, unless you use specialized SQL_MODE settings. This assumption was borne out by Kolbe Kegel’s comment on this post, and there are 30 …

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Implicit Commit Functions?

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 stored FUNCTION OR TRIGGER.

While an explicit COMMIT is obvious when placed inside a function, the implicit COMMIT statement isn’t obvious unless you know a DDL statement generates one. This means you can’t include any DDL statement inside a stored …

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Value or Reference?

In class today, we reviewed pass-by-value (IN-only mode) parameters and pass-by-reference (INOUT and OUT mode) parameters for stored procedures. The analogy that finally seemed to hit home for the students was linking the modes to the story of Alice in Wonderland.

Here’s the analogy and below is the code to support it:

“A pass-by-value parameter in a procedure is like sending an immutable copy of Alice into the rabbit hole, which means she can’t shrink, grow, or learn throughout the story; whereas, a pass-by-reference parameter in a procedure is like sending Alice into the rabbit hole where she can shrink, grow, fight the Jabberwocky, and learn things that make her life better when she exits the …

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Showing entries 1 to 7