Geekality » SQL

Oracle: Finding all constraints and their affected columns

Torleif — Thu, 12 Jan 2012 17:18:28 +0000

Found an SQL script to list all constraints in an Oracle database together with affected columns. Putting it here in case I need it again… Took a while to run, but sure beats having to look through all the table definitions to find what exactly is preventing me from deleting a row…

SELECT UC.OWNER
, UC.CONSTRAINT_NAME
, UCC1.TABLE_NAME||'.'||UCC1.COLUMN_NAME "CONSTRAINT_SOURCE"
, 'REFERENCES'
, UCC2.TABLE_NAME||'.'||UCC2.COLUMN_NAME "REFERENCES_COLUMN"
FROM USER_CONSTRAINTS uc
, USER_CONS_COLUMNS ucc1
, USER_CONS_COLUMNS ucc2
WHERE UC.CONSTRAINT_NAME = UCC1.CONSTRAINT_NAME
AND UC.R_CONSTRAINT_NAME = UCC2.CONSTRAINT_NAME
AND UCC1.POSITION = UCC2.POSITION -- Correction for multiple column primary keys.
AND UC.CONSTRAINT_TYPE = 'R'
ORDER BY UCC1.TABLE_NAME
, UC.CONSTRAINT_NAME;

If you’re just looking for one particular constraint you can of course also add and UC.CONSTRAINT_NAME = 'SOME NAME'

SQL for listing all WordPress tags

Torleif — Mon, 13 Jun 2011 20:47:17 +0000

When writing a post I sometimes find it difficult to choose what I should tag it with. I try reuse tags I already have to prevent a total mess, and sometimes I just don’t really remember what tags I have used so far. When writing a post in WordPress you can get a list of the most used ones, but once in a while I write a post on subject I haven’t written a lot about. So, instead of going to the Post Tags page and look through all the pages of tags, I decided to just connect to my blog database and run a query.

SELECT name, slug, description, COUNT FROM wp_terms
NATURAL JOIN wp_term_taxonomy
WHERE taxonomy="post_tag"
ORDER BY name

Lists all your tags, sorted by name

Oracle: How to search for a table or column in a big database

Torleif — Fri, 25 Mar 2011 07:54:43 +0000

I needed to find columns containing a certain string. That is, the name of the column should contain that string. Actually not too difficult to do

SELECT TABLE_NAME, column_name
FROM all_tab_columns
WHERE column_name LIKE '%FOO_ID%';

That gives you a nice list of all columns containing FOO_ID and what tables you find them in. Fantastic! Now, back to work…

MySQL: How to clone a table

Torleif — Fri, 04 Mar 2011 17:51:36 +0000

Ever wanted to, for some reason, clone a database table? Don’t really want to export anything or figure out what statement was used to create that table? Turns out that’s a lot easier to do than I thought it was.

Stumbled over a blog post on how you can copy a MySQL table with schema and keys, and boy was it easy.

CREATE TABLE newtable LIKE oldtable;

And that’s it! Want the data copied over as well?

INSERT INTO newtable SELECT * FROM oldtable;

Super easy!

How to delete WordPress post revisions

Torleif — Tue, 20 Oct 2009 21:40:23 +0000

Having revisions on my posts is nice I suppose. But I was starting to get a bit annoyed with the increasingly long list of revisions in each post. And they really did get long. Mainly because I am in a bit of a testing and experimenting phase which means that I have done a lot of adjustments to almost every single post so far because I don’t have 100% control on how I want things or how things will end up looking and so on There’s also of course all the obligatory spelling errors I only discover after I have clicked Publish

Anyways, I found a nice little MySQL snippet to clear out all of them in a French comment to a blog post. Thought I could share it here. That way I won’t lose it either

DELETE x,y,z
FROM wp_posts x
LEFT JOIN wp_term_relationships y ON (x.id = y.object_id)
LEFT JOIN wp_postmeta z ON (x.id = z.post_id)
WHERE x.post_type = 'revision'

You can swap delete x,y,z with select * to check that it will delete what you really want to.

Remember that if you have a table prefix other than ‘wp_’ set in your wp-config.php, you need to change that in your SQL script before you run it. The line looks like this in my config file:

$table_prefix = 'wp_';

I can also recommend setting WP_POST_REVISIONS to something in your wp-config.php file. Just search for REVISIONS in that file. If you don’t find it, you can just add it somewhere. The line should look like the following, where N would be how many revisions you want to allow, or -1 if you want them all:

define('WP_POST_REVISIONS', N);

I will still run the SQL script once in a while though, cause after a while my posts become sort of stable, and having revisions with my spelling errors hanging around for ever doesn’t really make sense in my head