inner join การใช้

• The choice to use an inner join depends on the database design and data characteristics.
• Only inner joins are supported and are specified by a comparison of columns from different tables.
• :INNER JOIN is SQL . You can code SQL into modules in a number of ways.
• Constructing those tables was a painful exercise in data storage and manipulation, inner joins and scripting.
• The join statement defines how disparate, hierarchical data formats are joined and is comparable to inner joins for relational databases.
• A left outer join can usually be substituted for an inner join when the join columns in one table may contain NULL values.
• The results of a cross join can be filtered by using a WHERE clause which may then produce the equivalent of an inner join.
• Depending on the desired results, this behavior may be a subtle bug, which can be avoided by replacing the inner join with an outer join.
• A complex SQL query that includes one or more inner joins and several outer joins has the same risk for NULL values in the inner join link columns.
• A complex SQL query that includes one or more inner joins and several outer joins has the same risk for NULL values in the inner join link columns.
• Conversely, an inner join can result in disastrously slow performance or even a server crash when used in a large volume query in combination with database functions in an SQL Where clause.
• Any data column that may be NULL ( empty ) should never be used as a link in an inner join, unless the intended result is to eliminate the rows with the NULL value.
• If NULL join columns are to be deliberately removed from the result set, an inner join can be faster than an outer join because the table join and filtering is done in a single step.
• The database may read and inner join the selected columns from both tables before reducing the number of rows using the filter that depends on a calculated value, resulting in a relatively enormous amount of inefficient processing.
• :It might be useful to note that that JOIN syntax ( the comma between tables is an implicit INNER JOIN ) assumes the ` sid ` column is present in both tables and that no other columns share a name.
• Every constraint can be viewed as a inner join of the tables representing its constraints; therefore, the problem of existence of solutions can be reformulated as the problem of checking whether the result of an inner join of a number of tables is empty.
• Every constraint can be viewed as a inner join of the tables representing its constraints; therefore, the problem of existence of solutions can be reformulated as the problem of checking whether the result of an inner join of a number of tables is empty.
• A commitment to SQL code containing inner joins assumes NULL join columns will not be introduced by future changes, including vendor updates, design changes and bulk processing outside of the application's data validation rules such as data conversions, migrations, bulk imports and merges.
• If you want to return records where there is only a result in one of the tables ( for example a document with no matching author record ) you will want to use outer joins instead of inner joins .  BradV 16 : 14, 20 February 2008 ( UTC)
• :Or, if that won't work : SELECT MRN, SBP, DBP FROM patients INNER JOIN visits ON visits . MRN = patients . MRN AND visits . id = ( SELECT ID FROM visits WHERE visits . MRN = patients . MRN ORDER BY Date DESC LIMIT 1)