It’s because the name column on the bar table does not have the UNIQUE constraint. So imagine you have 2 rows on the bar table that contain the name ‘ams’ and you insert a row on baz with ‘ams’ on bar_fk, which row on bar would it be referring since there are two rows matching?
The PARTITION BY clause sets the range of records that will be used for each “GROUP” within the OVER clause. In your example SQL, DEPT_COUNT will return the number of employees within that department for every employee record. (It is as if you’re de-nomalising the emp table; you still return every record in the emp table.) If there was another column (e.g., state) then you could … Read more
Yep, Oracle has temporary tables. Here is a link to an AskTom article describing them and here is the official oracle CREATE TABLE documentation. However, in Oracle, only the data in a temporary table is temporary. The table is a regular object visible to other sessions. It is a bad practice to frequently create and drop temporary tables in Oracle. Oracle … Read more
String literals Escaping single quotes ‘ by doubling them up -> ” is the standard way and works of course: Plain single quotes (ASCII / UTF-8 code 39), mind you, not backticks `, which have no special purpose in Postgres (unlike certain other RDBMS) and not double-quotes “, used for identifiers. In old versions or if you still run with standard_conforming_strings = … Read more
There are many tutorial articles about xml parsing with TSQL. For example, http://www.sqlserver.info/syntax/parse-xml-with-sql-server/
The proper way to do this is to use multiple tables and JOIN them in your queries. For example: The person_fruit table contains one row for each fruit a person is associated with and effectively links the person and fruits tables together, I.E. When you want to retrieve a person and all of their fruit … Read more
I suspect that you have two tables with the same name. One is owned by the schema ‘dbo’ (dbo.PerfDiag), and the other is owned by the default schema of the account used to connect to SQL Server (something like userid.PerfDiag). When you have an unqualified reference to a schema object (such as a table) — one … Read more
The value 3172978990 is greater than 2147483647 – the maximum value for INT – hence the error. MySQL integer types and their ranges are listed here. Also note that the (10) in INT(10) does not define the “size” of an integer. It specifies the display width of the column. This information is advisory only. To fix the error, change your datatype to VARCHAR. Phone and … Read more
Neither is possible in relational algebra but people have been creating some “extensions” for these operations (Note: in the original text, part of the text is written as subscript). GROUP BY, According to the book Fundamentals of Database Systems (Elmasri, Navathe 2011 6th ed): Another type of request that cannot be expressed in the basic … Read more