update pos
set a = concat_ws((select b from (select * from pos where a is not null limit 1) as ta), '', b)
where a is null
我要更新every row在专栏 a来自last value的b其值为b .
最佳答案
如果我理解正确，并且您正在使用 SQL Server，那么您正在寻找 LAG() 函数来获取 B 的先前值。弄清楚如何使用它。
https://msdn.microsoft.com/en-us/library/hh231256.aspx
Accesses data from a previous row in the same result set without the use of a self-join in SQL Server 2012. LAG provides access to a row at a given physical offset that comes before the current row. Use this analytic function in a SELECT statement to compare values in the current row with values in a previous row.
关于mysql - 如何从同一表中的另一列和行动态更新sql中的列，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30045971/