过滤与定位数据

Python 中的数据库入门

Jason Myers

Co-Author of Essential SQLAlchemy and Software Engineer

Where 子句

stmt = select([census])

stmt = stmt.where(census.columns.state == 'California')

results = connection.execute(stmt).fetchall()

for result in results:
    print(result.state, result.age)

California 0
California 1
California 2
California 3
California 4
California 5
...

Where 子句

基于布尔条件限制查询返回的数据
将列与某个值或另一列比较
常用比较：==、<=、>=、!=

表达式

提供比简单运算符更复杂的条件
如：in_()、like()、between()
更多请见文档
作为 Column 的方法提供

表达式

stmt = select([census])

stmt = stmt.where(census.columns.state.startswith('New'))

for result in connection.execute(stmt):
    print(result.state, result.pop2000)

New Jersey 56983
New Jersey 56686
New Jersey 57011
...

连接词

允许在 where 子句中使用多个条件
如：and_()、or_()、not_()

连接词

from sqlalchemy import or_

stmt = select([census])

stmt = stmt.where(
    or_(census.columns.state == 'California',
        census.columns.state == 'New York'
    )
)

for result in connection.execute(stmt):
    print(result.state, result.sex)

New York M
...
California F

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Python 中的数据库入门