Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 11: Writing Scripts and Batches
To expand our earlier example just a bit, let’s actually print a warning message out if we do not create
our table:
-- Now we’re run our conditional CREATE statement
IF NOT EXISTS (
SELECT s.name AS SchemaName, t.name AS TableName
FROM sys.schemas s
JOIN sys.tables t
ON s.schema_id = t.schema_id
WHERE s.name = ‘dbo’
AND t.name = ‘OurIFTest’
)
CREATE TABLE OurIFTest(
Col1 int PRIMARY KEY
);
ELSE
PRINT ‘WARNING: Skipping CREATE as table already exists’;
If you have already run the preceding example, then the table will already exist, and running this second
example should get you the warning message:
WARNING: Skipping CREATE as table already exists
Grouping Code into Blocks
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Sometimes you need to treat a group of statements as though they were all one statement (if you execute
one, then you execute them all — otherwise, you don’t execute any of them). For instance, the IF statement
will, by default, consider only the very next statement after the IF to be part of the conditional code.
What if you want the condition to require several statements to run? Life would be pretty miserable if you
had to create a separate IF statement for each line of code you wanted to run if the condition holds.
Thankfully, like most any language with an IF statement, SQL Server gives us a way to group code into
blocks that are considered to all belong together. The block is started when you issue a BEGIN statement
and continues until you issue an END statement. It works like this:
IF
BEGIN --First block of code starts here -- executes only if
--expression is TRUE
Statement that executes if expression is TRUE
Additional statements
...
...
Still going with statements from TRUE expression
IF --Only executes if this block is active
BEGIN
Statement that executes if both outside and inside
expressions are TRUE
Additional statements
...
...
Still statements from both TRUE expressions
END