barcode generator vb.net free Such a statement tests for the presence of the records in the subquery. in Software

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Such a statement tests for the presence of the records in the subquery.
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Basic Transact-SQL Programming Constructs
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The stored procedure prInsertEquipment can be modified to use the Exists keyword:
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. . . If Exists (Select EqTypeId From EqType Where EqType = @chvEqType) . . .
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Naturally, if you use the Not operator, the encapsulated statement will be executed if the subquery does not return records:
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Alter Procedure prInsertEquipment_2 -- store values in equipment table. -- return identifier of the record to the caller. ( @chvMake varchar(50), @chvModel varchar(50), @chvEqType varchar(30) ) As declare @intEqTypeId int, @intEquipmentId int
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-- does such eqType already exists in the database If Not Exists (Select EqTypeId From EqType Where EqType = @chvEqType) --if it does not exist Begin -- insert new EqType in the database Insert EqType (EqType) Values (@chvEqType) -- get id of record that you've just inserted Select @intEqTypeId = @@identity End else -- read Id of EqType Select @intEqTypeId From EqType Where EqType = @chvEqType --insert equipment Insert Equipment (Make, Model, EqTypeId) Values (@chvMake, @chvModel, @intEqTypeId)
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Select @intEquipmentId = @@identity -- return id to the caller Return @intEquipmentId
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If statements can be nested. In fact, both If and Else can be nested:
Create Procedure prInsertEquipment_3 -- store values in equipment table. -- return identifier of the record to the caller. ( @chvMake varchar(50), @chvModel varchar(50), @chvEqType varchar(30), @intEquipmentId int ) As declare @intEqTypeId int, @ErrorCode int -- does such eqType already exists in the database If Not Exists (Select EqTypeId From EqType Where EqType = @chvEqType) --if it does not exist Begin -- insert new EqType in the database Insert EqType (EqType) Values (@chvEqType) -- get id of record that you've just inserted Select @intEqTypeId = @@identity, @ErrorCode = @@Error If @ErrorCode <> 0 begin Select 'Unable to insert Equipment Type. Error: ', @ErrorCode Return 1 End End Else Begin -- read Id of EqType
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Basic Transact-SQL Programming Constructs
Select @intEqTypeId From EqType Where EqType = @chvEqType Select @ErrorCode = @@Error If @ErrorCode <> 0 begin Select 'Unable to get Id of Equipment Type. Error: ', @ErrorCode Return 2 End End --insert equipment Insert Equipment (Make, Model, EqTypeId) Values (@chvMake, @chvModel, @intEqTypeId) Select @ErrorCode = @@Error If @ErrorCode <> 0 Begin Select 'Unable to insert Equipment. Error: ', @ErrorCode Return 3 End -- return id to the caller Select @intEquipmentId = @@identity Return 0
There is no limit to the number of levels. However, this capability should not be abused. The presence of too many levels is a sure sign that a more in-depth study should be made concerning code design.
Looping the While Statement
Transact-SQL contains only one statement that allows looping:
While Boolean_expression {sql_statement | statement_block} [Break]
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{sql_statement | statement_block} [Continue]
If the value of the Boolean expression is True (1), the server will execute one or more encapsulated Transact-SQL statement(s). From inside the block of statements, this execution can be controlled with the Break and Continue statements. The server will interrupt the looping when it encounters a Break statement. When the server encounters a Continue statement, it will ignore the rest of the statements and restart the loop.
NOTE: Keep in mind that loops are primarily tools for third-generation languages. In such languages, code was written to operate with records one at a time. Transact-SQL is a fourth-generation language and is written to operate with sets of information. It is possible to write code in Transact-SQL that will loop through records and perform operations on a single record, but you pay for this feature with severe performance penalties. However, there are cases when such an approach is necessary.
It is not easy to find bona fide examples to justify the use of loops in Transact-SQL. Let us investigate a stored procedure that calculates the factorial of an integer number:
Create Procedure prCalcFactorial -- calculate factorial -- 1! = 1 -- 3! = 3 * 2 * 1 -- n! = n * (n-1)* . . . 5 * 4 * 3 * 2 * 1 @N tinyint, @F int OUTPUT As Set @F = 1 while @N > 1 begin set @F = @F * @N Set @N = @N - 1 end return 0
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