Two columns, and recognizes only one such column with the given name. Names for the column in the USING clause. USING clause tells Oracle that the tables in the join have identical The USING clause affects the semantics of the SELECT clause. This join query can be rewritten as: SELECT location_id, department.name, location.regional_group Tables, and its value must be the same in both tables. ( location_id) is named identically in both the The column involved in the join condition ON department.location_id = location.location_id Of a join query: SELECT department.location_id, department.name, location.regional_group If these two conditions are satisfied, you can apply the USING clause The names of the join columns are identical in both the tables. The join depends on an equality condition between two columns, orīetween sets of two columns, to relate the rows from the two tables. Specifying the joinĬondition can be simplified if the following conditions hold true: Was specified in the ON clause, which contained an expressionĭefining the relationship between the two tables. In this chapter's first example, the join condition Involving other operators are discussed later in this chapter in Section 3.3.4. A join condition may contain other operators as well. It is not necessary that a join condition involve the equal-to (=) Oracle performs implicit data type conversion The data types of the columns involved in a join condition need to be The total number of join conditions in a query is always equal to the The case when a foreign key constraint consists of multiple columns. Involves columns that relate two tables in some logical way.Ī join condition may involve more than one column.

However, you can join on other columns as well. One table and the primary key or unique key columns of another table. Usually a join condition is specified on the foreign key columns of It is a good practice to use tableĪliases everywhere in a query if you are using them at all. With the columns in the SELECT clause as well, even though thoseĬolumn names are unambiguous. Therefore, the table aliasesĬlause to ask Oracle to equate the location_idĬolumn from the department table with the In this example, the column name location_idĪppears in both the tables. For example: SELECT d.dept_id, d.name, l.regional_group Table name) to qualify any ambiguous column name. Whenever there is anĪmbiguity in the column names, you must use a table alias (or the When selecting data from multiple tables. However, the location_id column is not selected: SELECT d.dept_id, d.name, l.regional_group In the following example, the join condition The columns specified in a join condition need not be specified in Some of the things that you should knowĪbout join conditions are discussed in the following list: This process is repeated for all combinations of The join condition is true, Oracle includes this combination of rows Two tables, and checks to see whether the join condition is true. To perform the join, Oracle picks up one combination of rows from the Location table: ON department.location_id = location.location_id In the previous example, the ON clause specifies the joinĬondition by which the location_id column of the This join condition is usually applied to the foreign keyĬolumns of one table and the primary or unique key columns of another The rows from one table will be combined with the rows of another Join query, you specify a condition that conveys a relationshipīetween the tables specified in the FROM clause.

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