I want to log the full SQL query of anything changing the value of one column from one pre-determined value to another pre-determined value. Unfortunately, it is unclear to me how to do this, if it even is at all.
Any ideas?
Thanks!
Set up an update trigger (after or before) on the table.
Then have logic (expressed as pseudo-code):
if old.col = 'Value1' and new.col = 'Value2'
then insert into logrecords(. . .) select "what I want to log here"
end if ;
MySQL Proxy can help you to get the query and you can write a filter to select queries only that are affecting specific rows.
Related
I'm trying select all values if such table exists. If it doesn't exist, just leave it.
I'm trying to do this only in one MYSQL code. Not with the help of python or something.
SELECT CASE WHEN (SELECT count(*)
FROM information_schema.TABLES
WHERE TABLE_SCHEMA = '{db0}' AND TABLE_NAME = '{table0}')=0
THEN 'None' ELSE (SELECT MAX({colname}) FROM {db0}.{table0}) END;
If i inject existing table name on it, it works well.
But if not , it shows the error sign that saying such table doesn't exist.(Table 'corps.060311' doesn't exist)
What should I do?
This cannot be achieved using a simple query because MySQL analyses the query as a whole before performing it: it is not a procedural language and the queries are never executed line by line.
To do what you want to do without help of any other language, you must use stored procedures: https://dev.mysql.com/doc/refman/8.0/en/create-procedure.html
So the first step is to add a new FUNCTION in your database that will contain the "if table exists" part (see https://dev.mysql.com/doc/refman/8.0/en/if.html for if statements) and will return the desired value based on the schema, table, and column provided as strings in input of the function.
Then you can use the FUNCTION in any query in your database.
When I try to create a simple update query with Subtraction or anything else in the same table, it doesn't return me any value, could it be something to do with formating?
This is SQL code: UPDATE Sales SET Sales.GrossProfit = [SubTot]-[Cost];
It doesn't return any value.
I have copied syntax from different databases (from colleagues) where the same type of query worked. Could it be something to do with my general Access settings?
UPDATE Sales SET Sales.GrossProfit = [SubTot]-[Cost];
I expect the query to update the GrossProfit column with the calculation "SubTot - Cost"
Strictly speaking, an UPDATE query does not "return" any columns. It only changes data in existing rows, but by itself does not return those changes back to you. (It is more accurately called an Update statement since it does not return data.)
For instance, if you were to execute the UPDATE statement in VBA code, you would not get a RecordSet of columns like with a SELECT query. To get the results after executing the UPDATE statement would require that you execute a separate SELECT query.
However, I assume that you are viewing the Update query in the Access query designer. Correct?
In that case, when you click on the View button (Datasheet View), Access tries to be smart & useful about the UPDATE and converts it temporarily into a SELECT query so that you can visualize the existing data in the columns. The Datasheet View does not actually run the UPDATE statement, nor does it show a preview of what will happen when you do run it.
While in Design View or SQL View for an Update query (or for Delete, Make Table, and Append queries), there is a Run button with a red exclamation point (on the Design ribbon/toolbar). Clicking that button will actually execute the query that changes the table values. Although it will not show you results row by row, you should get a pop-up telling you how many rows were changed due to the statement. (You may also get confirmation prompts that the statement is about to change data in the table.)
I have several tables that have a common field (column) called LastName in a MySQL database. Several of the rows in these tables are in mixed case so they don't get selected properly when doing a SELECT.
How can I convert those columns to all UPPER CASE? I can easily handle any new entries to convert them to upper case, but the existing records I'm not so sure about.
would do the job
update table set LastName=UPPER(LastName);
NOTE - if you are running from MySQL workbench you may have to disable safety mode or add a where clause (eg WHERE id>0) otherwise it wont run.
this would work:
UPDATE table_name SET `column_name` = UPPER( `column_name` )
You can use the string function UPPER() to make the column value to upper
update Your_table set LastName=UPPER(LastName)
Is there an easy way to get the id of the row that was affected by an update statement from DBI? In this particular case, it will always be either 0 or 1 row. I didn't want the expense of having to redo the selection part of the query again to get the data, as it is kind of costly.
I am have to do the update first, because otherwise I introduce the possibility of a race-time condition between the select and the update.
You might want to read this related SO topic (I've linked to the answer by #Erwin Brandstetter) -- this is the way I've always handled it.
Depending on your database engine, you are likely to have a SELECT ... FOR UPDATE facility. You should use this to
SELECT ... FOR UPDATE the record you want to update
Save the ID from the record, and do the UPDATE using the ID instead of the original criteria
The MySQL documentation about SELECT ... FOR UPDATE may helps you, working with transactions.
I have just noticed that where mysql_num_rows should return the number of rows returned for either SELECT or SHOW commands, returns 0 for SHOW TABLE command specifically.
Instead it shows the affected rows count instead of the num rows.
Can anyone please tell me if this is a bug or if am I missing anything here?
SHOW TABLE command is used to Show you table name in your database . On the other hand , mysql_num_rows is used to count how many result got from your query. This query is depend on your requirement basis ...
As stated on the PHP documentation page:
Retrieves the number of rows from a result set. This command is only
valid for statements like SELECT or SHOW that return an actual result
set.
My guess is that SHOW TABLES is not a technical query that would produce the type of result set that mysql_num_rows enumerates.
These "helper" functions (such as SHOW, EXPLAIN, DESCRIBE etc.) won't let you issue their results like you would in a regular table.
But if you're looking for how you can do this, for SHOW TABLES you can do
SELECT `table_name` FROM `information_schema`.`tables`
WHERE `table_schema`=DATABASE()
-- DATABASE() selects current database name
-- you can use the name of any database as a string instead
So basically you can use the information_schema database to get that information.
It was a bug in mysql, fixed it with the update.