sql expression builder

common table expression (CTE), in which the use of a CTE enables the maintainability of the SQL statement, while the CTE is much more efficient than the table variable. The following is the syntax for a CTE: Copy Code code as follows: [With Expression_name [(column_name [, N])] As (cte_query_definition) Now using a CTE to solve the problem above, the

right-hand side behavior the result of the operator generates NULL, then the result of any construct will be null instead of FALSE. This behavior is determined in accordance with the rules of SQL handling Boolean and NULL values.As with EXISTS, it is unwise to assume that subqueries will be completed. Row_constructor operator ANY (subquery) Row_constructor operator SOME (subquery) This form of the left-hand side is a row

statement uses a subquery. Although this SQL statement is not complex, if there are too many layers of nesting, it will make the SQL statement very difficult to read and maintain. Therefore, you can use table variables to solve this problem. The SQL statement is as follows: Declare @ t table (countryregioncode nvarchar (3 ))Insert into @ T (countryregioncode) (s

like 'C % ') Select * from person. StateProvince where CountryRegionCodeIn (select * from @ t) Although the preceding SQL statement is more complex than the first method, the subquery is placed in the table variable @ t. This will make the SQL statement easier to maintain, however, there will be another problem. The server space is the performance loss. Because the table variables actually use temporary ta

Recursive queries using CTE (common table expressions) ---- SQL Server 2005 and later versions A common table expression (CTE) has an important advantage: It can reference itself to create a recursive CTE. Recursive CTE is a public table expression that repeats the initial CTE to return a subset of data until the complete result set is obtained. When a query refe

We often encounter some special requirements in projects. For example, the drop-down box is checked, and the query conditions are spliced according to the option in the drop-down box. After you see this picture, you will surely say that this is very simple. Combine all the options into "1-3" and "5-9" and put them behind the words in. This is indeed logically correct, but have you ever thought about this problem? excessive coupling with the business can solve it? The current demand sacrifices c

about another problem, namely the performance loss. Because the table variables actually use temporary tables, which increases Additional I/O overhead, the table variables are not suitable for large data volumes and frequent queries. Therefore, another solution is provided in SQL Server 2005, which is the common table expression (CTE). Using CTE can make the SQL

We often encounter some special requirements in projects. For example, the drop-down box is checked, and the query conditions are spliced according to the option in the drop-down box. After you see this picture, you will surely say that this is very simple.Combine all the options into "1-3" and "5-9" and put them behind the words in.This is indeed logically correct, but have you ever thought about this problem? excessive coupling with the business can solve it?The current demand sacrifices code

frequently. To do this, another solution is provided in SQL Server 2005, which is a common table expression (CTE) that uses a CTE to make the SQL statement maintainable, while the CTE is much more efficient than a table variable.Here is the syntax for the CTE: [With Now using the CTE to solve the above problem, the SQL