即使查询不是通过网络发送，SELECT *也是一种糟糕的做法。

Selecting more data than you need makes the query less efficient - the server has to read and transfer extra data, so it takes time and creates unnecessary load on the system (not only the network, as others mentioned, but also disk, CPU etc.). Additionally, the server is unable to optimize the query as well as it might (for example, use covering index for the query). After some time your table structure might change, so SELECT * will return a different set of columns. So, your application might get a dataset of unexpected structure and break somewhere downstream. Explicitly stating the columns guarantees that you either get a dataset of known structure, or get a clear error on the database level (like 'column not found').

当然，对于一个小而简单的系统来说，所有这些都不太重要。

在某些情况下，SELECT *适用于维护目的，但一般情况下应该避免使用。

These are special cases like views or stored procedures where you want changes in underlying tables to propagate without needing to go and change every view and stored proc which uses the table. Even then, this can cause problems itself, like in the case where you have two views which are joined. One underlying table changes and now the view is ambiguous because both tables have a column with the same name. (Note this can happen any time you don't qualify all your columns with table prefixes). Even with prefixes, if you have a construct like:

选择A.， B. -您可能会遇到客户端现在难以选择正确字段的问题。

一般来说，我不使用SELECT *，除非我在做一个有意识的设计决策，并指望相关的风险很低。

为应用程序中期望获得的每一列命名还可以确保如果有人更改表，只要您的列仍然存在(以任何顺序)，应用程序就不会崩溃。

指定列列表通常是最好的选择，因为如果有人向表中添加/插入列，您的应用程序不会受到影响。

为了补充其他人所说的，如果您选择的所有列都包含在一个索引中，则结果集将从索引中提取，而不是从SQL中查找其他数据。

指定你需要的列总是更好的，如果你想一次，SQL不必每次查询都想着“wtf是*”。最重要的是，稍后有人可能会向表中添加您在查询中实际上不需要的列，在这种情况下，通过指定所有列会更好。