SQL statements are case-insensitive, meaning they can be written using lowercase, uppercase or a combination. However, it is customary to write out SQL keywords -- commands or control operators -- in all-caps and table/column names in lowercase. Words in the statement can be treated as case...
This size factor also has implications in determining what key you should choose from a dimension table to maintain the fact table/dimension table relationships. Composite keys based on the business key of the dimension—meaning the real-world identifier of the entity represented by the dimension—...
Outer joins are directional, meaning you can specify whether to include all the records from the first table specified in the join (called a left join), or to include all the records from the second table in the join (called a right join). An outer join has the following ...
the MySQL optimizer considers many techniques to efficiently perform the lookups involved in an SQL query. A query on a huge【hjuːdʒ巨大的;非常成功的;极多的;走红的;程度高的;】 table can be performed without reading all the rows; a join involving several tables can be ...
SQL Copy SELECT ProductID, ProductModelID FROM Production.Product WHERE ProductModelID = 20 OR ProductModelID = 21 AND Color = 'Red'; GO You can change the meaning of the query by adding parentheses to force evaluation of the OR first. The following query finds only products under model...
SQL Copy SELECT ProductID, ProductModelID FROM Production.Product WHERE ProductModelID = 20 OR ProductModelID = 21 AND Color = 'Red'; GO You can change the meaning of the query by adding parentheses to force evaluation of the OR first. The following query finds only products under models...
!inNot equal to any of the elements The list of string operators is a longer list because it has permutations for case sensitivity, substring locations, prefixes, suffixes, and much more. The==operator is both a numeric and string operator, meaning it can be used for both numbers and text...
"explicit value must be specified for identity column in table" error in SQL 2000 "FROM clause have the same exposed names. Use correlation names to distinguish them" "No transaction is active." error when trying to send a transactional SQL statment over MSDTC "Restricted data type attribute ...
(nested loop, hash, merge) and you’ll see why optimization is such an important concept in SQL. SQL Server uses a cost based optimizer, meaning that it will consider all (or at least many) of the possible alternatives, try to make an educated guess about the cost of each alternative,...
changes made via a path through one variable are immediately visible through the other. Rows in a relational database table do not have unique identity. However, they do have a primary key and that primary key may be unique, meaning no two rows may share the same key. Yet this only cons...