One-to-one: Use a foreign key to the referenced table: You must also put a unique constraint on the foreign key column (addess.student_id) to prevent multiple rows in the child table (address) from relating to the same row in the referenced table (student). One-to-many: Use a foreign key on the many side of the relationship linking back … Read more
There are mainly three types of variables in MySQL: User-defined variables (prefixed with @):You can access any user-defined variable without declaring it or initializing it. If you refer to a variable that has not been initialized, it has a value of NULL and a type of string.SELECT @var_any_var_name You can initialize a variable using SET or SELECT statement:SET @start = 1, @finish = … Read more
May be this will help you.
Should you instead be setting the identity insert to on within the stored procedure? It looks like you’re setting it to on only when changing the stored procedure, not when actually calling it. Try:
Yes, something like this: As other answers have pointed out, MySQL also has the IF() function to do this using less verbose syntax. I generally try to avoid this because it is a MySQL-specific extension to SQL that isn’t generally supported elsewhere. CASE is standard SQL and is much more portable across different database engines, and I prefer to … Read more
VARCHAR is variable-length. CHAR is fixed length. If your content is a fixed size, you’ll get better performance with CHAR. See the MySQL page on CHAR and VARCHAR Types for a detailed explanation (be sure to also read the comments).
Single quotes are escaped by doubling them up, just as you’ve shown us in your example. The following SQL illustrates this functionality. I tested it on SQL Server 2008: Results
Quite simple actually: The % is a wildcard for any characters set (none, one or many). Do note that this can get slow on very large datasets so if your database grows you’ll need to use fulltext indices.
Rather slow, but working method to include any of words: If you need all words to be present, use this: If you want something faster, you need to look into full text search, and this is very specific for each database type.
Group By X means put all those with the same value for X in the one group. Group By X, Y means put all those with the same values for both X and Y in the one group. To illustrate using an example, let’s say we have the following table, to do with who is attending what subject at … Read more