It’s the free web-edition of SQL Performance Explained, regarding SQL indexing and tuning for DB2, MySQL, Oracle, PostgreSQL, and SQL Server.

SQL indexing is the most effective tuning method—yet it is often neglected during development. Use The Index, Luke explains SQL indexing from grounds up and doesn’t stop at ORM tools like Hibernate.

Use The Index, Luke is the free web-edition of SQL Performance Explained. If you like this site, consider getting the book. Also have a look at the shop for other cool stuff that supports this site.

/via Use the Index, Luke/

How does it work?

More specifically,

• Connect to your database.
• Refresh with the current structure of your database.
• Database Note Taker shows where documentation is missing.
• Add and edit notes for tables, columns, stored procedures and so on.
• Publish and distribute the documentation.
• When your database has changed, refresh and add new notes.

Features

Here are a few features worth mentioning:

• Separate documentation
• Work offline – a live database connection is only required to refresh the database.
• Publish to HTML
• Database platform independent
• Source control friendly
• Search
• Multiple developers friendly
• History tracking
• etc.

Not enough and looking for more database documentation options? Check out this list compiled by SQLShark.

List the name of all the tables in a database

USE databasename
SELECT * FROM information_schema.tables ORDER BY TABLE_NAME

Replace the real database name in, you are off to go to get a list of tables in that database in the order of the table name.

List the column names of all the tables in a database

Now since we know how many tables in a database, let’s find out what the columns are in each table.

USE databasename
SELECT t.name AS table_name,
SCHEMA_NAME(schema_id) AS schema_name,
c.name AS column_name
FROM sys.tables AS t
INNER JOIN sys.columns c ON t.OBJECT_ID = c.OBJECT_ID 
ORDER BY schema_name, table_name;

If you need to know the column details in each table, do the following to each table:

exec sp_columns 'table1'
exec sp_columns 'table2'
...
...

List the tables with row counts and space consumption

If you are investigating a fairly large database, it would be helpful knowing what tables to look first. Execute the following statements and you will get a more clear picture of what you should look into first.

Use databasename
SELECT 
    t.NAME AS billings,
    s.Name AS SchemaName,
    p.rows AS RowCounts,
    SUM(a.total_pages) * 8 AS TotalSpaceKB, 
    SUM(a.used_pages) * 8 AS UsedSpaceKB, 
    (SUM(a.total_pages) - SUM(a.used_pages)) * 8 AS UnusedSpaceKB
FROM 
    sys.tables t
INNER JOIN      
    sys.indexes i ON t.OBJECT_ID = i.object_id
INNER JOIN 
    sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id
INNER JOIN 
    sys.allocation_units a ON p.partition_id = a.container_id
LEFT OUTER JOIN 
    sys.schemas s ON t.schema_id = s.schema_id
WHERE 
    t.NAME NOT LIKE 'dt%' 
    AND t.is_ms_shipped = 0
    AND i.OBJECT_ID > 255 
GROUP BY 
    t.Name, s.Name, p.Rows
ORDER BY 
    t.Name

That’s about it. These statements have helped me a lot in number of occasions where I need to figure out a new database in order to do some customization. I hope they will help you too down the road.

Meaning that there is no way of identifying them who is who. Usually, it happens when the table doesn’t have a unique id field due to the poor database design. Because of that, there is no way in SQL to delete one of these duplications without deleting them all first.

You can copy the whole table into a new table first,

SELECT DISTINCT * INTO newTable FROM oldTable

And then, delete the old table and move all the records back but this time make sure you have the unique identifier set up as one field.

Scenario 2, similar records

The records have one field that is the same each other and only one copy needs to be preserved. Usually, they have the unique identifier set up to identify one to another. Then, try

DELETE t1 FROM oldTable AS t1, oldTable AS t2
WHERE (t1.duplicateField = t2.duplicateField )
AND (t1.uniqueidentifier > t2.uniqueidentifier)

As a side note, if you run into a program in which you keep getting message telling you that

If this is intended as a part of a table hint, A WITH keyword and parenthesis are now required.

that’s because one of the fields has the same name reserved as keywords in SQL server. You should put “[“ and “]” around it to tell the server that this is not a reserved keyword.