SQL WITH clause example - Stack Overflow
2012年9月23日 · The SQL WITH clause was introduced by Oracle in the Oracle 9i release 2 database. The SQL WITH clause allows you to give a sub-query block a name (a process also called sub-query refactoring), which can be referenced in several places within the main SQL query. The name assigned to the sub-query is treated as though it was an inline view or table.
sql - NOT IN vs NOT EXISTS - Stack Overflow
2007年5月18日 · In order to filter the student records that have a 10 grade in Math, we can use the EXISTS SQL operator, like this: SELECT id, first_name, last_name FROM student WHERE EXISTS ( SELECT 1 FROM student_grade WHERE student_grade.student_id = student.id AND student_grade.grade = 10 AND student_grade.class_name = 'Math' ) ORDER BY id
How do I perform an IF...THEN in an SQL SELECT?
2008年9月15日 · Both IIF() and CASE resolve as expressions within a SQL statement and can only be used in well-defined places. The CASE expression cannot be used to control the flow of execution of Transact-SQL statements, statement blocks, …
sql - How to implement one-to-one, one-to-many and many-to …
2022年1月28日 · Here are some real-world examples of the types of relationships: One-to-one (1:1) A relationship is one-to-one if and only if one record from table A is related to a maximum of one record in table B. To establish a one-to-one relationship, the primary key of table B (with no orphan record) must be the secondary key of table A (with orphan records).
A practical example of denormalization in a SQL database?
2019年11月26日 · CREATE TABLE AS ... SELECT is supported by all popular SQL implementations. I checked MySQL, PostgreSQL, SQLite, Oracle, Microsoft, and IBM DB2, and they all support it. I also find this syntax in a copy of the ISO SQL 2011 standard. –
sql - Oracle "Partition By" Keyword - Stack Overflow
2016年10月28日 · It is the SQL extension called analytics. The "over" in the select statement tells oracle that the function is a analytical function, not a group by function. The advantage to using analytics is that you can collect sums, counts, and a lot more with just one pass through of the data instead of looping through the data with sub selects or worse ...
SQL comment header examples - Stack Overflow
On a side note, any comments that I place within the SQL i always use the format: /* Comment */ As in the past I had problems where scripting (by SQL Server) does funny things wrapping lines round and comments starting -- have commented out required SQL.... but that might just be me.
Using RegEx in SQL Server - Stack Overflow
2012年1月19日 · On-prem Microsoft SQL Server will gain the same regex feature in the next major release ("vNext" as they say; so, that'll be SQL Server 2025 presumably). The new set of functions is somewhat documented in this community posting, but no reference for these functions yet exists in the main official documentation.
How do SQL EXISTS statements work? - Stack Overflow
2013年11月18日 · In order to filter the student records that have a 10 grade in Math, we can use the EXISTS SQL operator, like this: SELECT id, first_name, last_name FROM student WHERE EXISTS ( SELECT 1 FROM student_grade WHERE student_grade.student_id = student.id AND student_grade.grade = 10 AND student_grade.class_name = 'Math' ) ORDER BY id
Real life example, when to use OUTER / CROSS APPLY in SQL
Some uses for APPLY are.... 1) Top N per group queries (can be more efficient for some cardinalities) SELECT pr.name, pa.name FROM sys.procedures pr OUTER APPLY (SELECT TOP 2 * FROM sys.parameters pa WHERE pa.object_id = pr.object_id ORDER BY pr.name) pa ORDER BY pr.name, pa.name