我们所有使用关系数据库的人都知道(或正在学习)SQL是不同的。获得期望的结果,并有效地这样做,涉及到一个乏味的过程,其部分特征是学习不熟悉的范例,并发现一些我们最熟悉的编程模式在这里不起作用。常见的反模式是什么?


当前回答

使用SP作为存储过程名称的前缀,因为它将首先在系统过程位置中搜索,而不是自定义过程。

其他回答

使用SP作为存储过程名称的前缀,因为它将首先在系统过程位置中搜索,而不是自定义过程。

select some_column, ...
from some_table
group by some_column

假设结果将按some_column排序。我在Sybase上看到过这种情况,其中假设成立(目前)。

有一张桌子

code_1
value_1
code_2
value_2
...
code_10
value_10

而不是有3个表

Code, value和code_value

你永远不知道什么时候你可能需要10对以上的代码,价值。

如果只需要一对,就不会浪费磁盘空间。

我最不喜欢的是

Using spaces when creating tables, sprocs etc. I'm fine with CamelCase or under_scores and singular or plurals and UPPERCASE or lowercase but having to refer to a table or column [with spaces], especially if [ it is oddly spaced] (yes, I've run into this) really irritates me. Denormalized data. A table doesn't have to be perfectly normalized, but when I run into a table of employees that has information about their current evaluation score or their primary anything, it tells me that I will probably need to make a separate table at some point and then try to keep them synced. I will normalize the data first and then if I see a place where denormalization helps, I'll consider it. Overuse of either views or cursors. Views have a purpose, but when each table is wrapped in a view it's too much. I've had to use cursors a few times, but generally you can use other mechanisms for this. Access. Can a program be an anti-pattern? We have SQL Server at my work, but a number of people use access due to it's availabilty, "ease of use" and "friendliness" to non-technical users. There is too much here to go into, but if you've been in a similar environment, you know.

使用SQL作为美化的ISAM(索引顺序访问方法)包。特别是嵌套游标,而不是将SQL语句组合成一个更大的语句。这也算“滥用优化器”,因为实际上优化器能做的不多。这可以与非准备语句结合使用,以获得最大的效率:

DECLARE c1 CURSOR FOR SELECT Col1, Col2, Col3 FROM Table1

FOREACH c1 INTO a.col1, a.col2, a.col3
    DECLARE c2 CURSOR FOR
        SELECT Item1, Item2, Item3
            FROM Table2
            WHERE Table2.Item1 = a.col2
    FOREACH c2 INTO b.item1, b.item2, b.item3
        ...process data from records a and b...
    END FOREACH
END FOREACH

正确的解决方案(几乎总是)是将两个SELECT语句合并为一个:

DECLARE c1 CURSOR FOR
    SELECT Col1, Col2, Col3, Item1, Item2, Item3
        FROM Table1, Table2
        WHERE Table2.Item1 = Table1.Col2
        -- ORDER BY Table1.Col1, Table2.Item1

FOREACH c1 INTO a.col1, a.col2, a.col3, b.item1, b.item2, b.item3
    ...process data from records a and b...
END FOREACH

双循环版本的唯一优点是,您可以很容易地发现表1中值之间的中断,因为内部循环结束了。这可能是控制中断报告中的一个因素。

此外,应用程序中的排序通常是不允许的。