Question

希望你能提供帮助。没有显示整个查询，因为我不认为它是必需的但是想尝试查询以查看'street'中有空值，然后查看'free address'并将结果放在那里。我猜它涉及案例表达或concat

当前结果

SELECT

IdNum
street
free address

from ID


IdNum          street                  free address
  1          stack over flow               null
  2             null                   stack exchange
  3           downing street               null

必需结果 - 不需要显示注释免费地址栏，仅用于演示。

 IdNum          street                    free address
   1         stack over flow                  null
   2         stack exchange                stack exchange
   3         downing street                   null

非常感谢您的帮助

Answer 1

COALESCE()函数执行此操作：

SELECT IdNum,
       COALESCE(street, free_address) as street,
       free_address
FROM ID;

注意：ID是表格的奇怪名称，free address不是有效的列名称（因为空格）。

COALESCE()是ANSI标准函数，基本上可用于所有数据库。

Answer 2

使用$ node > []+[] '' > {}+{} '[object Object][object Object]' > []+{} '[object Object]' > {}+[] 0 > []-[] 0 > {}-{} NaN > []-{} NaN > {}-[] -0 > []*[] 0 > {}*{} NaN > []*{} NaN > {}*[] ... ^C > []/[] NaN > {}/{} NaN > []/{} NaN > {}/[] SyntaxError: Invalid regular expression: missing / at Object.exports.createScript (vm.js:24:10) at REPLServer.defaultEval (repl.js:137:25) at bound (domain.js:250:14) at REPLServer.runBound [as eval] (domain.js:263:12) at REPLServer.<anonymous> (repl.js:392:12) at emitOne (events.js:82:20) at REPLServer.emit (events.js:169:7) at REPLServer.Interface._onLine (readline.js:210:10) at REPLServer.Interface._line (readline.js:546:8) at REPLServer.Interface._ttyWrite (readline.js:823:14)功能，可以用您选择的替代方案替换COALESCE()值：

NULL

Answer 3

您可以使用CASE，COALESCE或（在SQL-Server中）ISNULL：

SELECT IdNum,
       CASE WHEN street IS NULL THEN free_address ELSE street END as street,
       free_address
FROM ID;

SELECT IdNum,
       COALESCE(street, free_address) as street,
       free_address
FROM ID;

SELECT IdNum,
       ISNULL(street, free_address) as street,
       free_address
FROM ID;

Answer 4

根据您使用的数据库，您可以使用ISNULL，NVL，IFNULL或COALESCE。

在此处选择正确的：SQL NULL Functions at w3schools

Answer 5

如果使用SQL Server

，可以使用以下命令

Select [IdNum], 
Case 
When [street] Is Null AND [free address] Is Not Null 
Then [free address] else [street] END As 'street',
[free address]
from ID

当一列为null时，从其他列获取数据

5 个答案: