Oracle 数据集

Oracle 在表与表之间取交集，差集关键字

UNION, UNION ALL, INTERSECT, and MINUS

You can combine multiple queries using the set operators UNION, UNION ALL, INTERSECT, and MINUS. All set operators have equal precedence. If a SQL statement contains multiple set operators, then Oracle Database evaluates them from the left to right unless parentheses explicitly specify another order.

The corresponding expressions in the select lists of the component queries of a compound query must match in number and must be in the same datatype group (such as numeric or character).

If component queries select character data, then the datatype of the return values are determined as follows:

If both queries select values of datatype CHAR of equal length, then the returned values have datatype CHAR of that length. If the queries select values of CHAR with different lengths, then the returned value is VARCHAR2 with the length of the larger CHAR value.

If either or both of the queries select values of datatype VARCHAR2, then the returned values have datatype VARCHAR2.

If component queries select numeric data, then the datatype of the return values is determined by numeric precedence:

If any query selects values of type BINARY_DOUBLE, then the returned values have datatype BINARY_DOUBLE.

If no query selects values of type BINARY_DOUBLE but any query selects values of type BINARY_FLOAT, then the returned values have datatype BINARY_FLOAT.

If all queries select values of type NUMBER, then the returned values have datatype NUMBER.

In queries using set operators, Oracle does not perform implicit conversion across datatype groups. Therefore, if the corresponding expressions of component queries resolve to both character data and numeric data, Oracle returns an error.