sql语句查询出现错误:unknown column,但是语句字段确实存在。很多语句...
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发布时间：2022-04-26 18:40
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时间：2022-05-03 06:54
CS0436 异常警告,vs中有可能是自己引用自己造成的)
批量替换
update 表名 set code=replace(code,原来值,修改值) where countyid=‘‘;
sql 截取字符串
https://www.cnblogs.com/xielong/p/7670757.html
substr(SUBITEM,instr(SUBITEM,‘*‘,1)+1)
其中，使用了substr函数和instr函数。
1、substr(string,start_position,[length])求子字符串，返回字符串
第一个参数表示要截取的字符串，第二个表示起始位置，第三个表示截取的长度，可省略。
2、instr(string,subString,position,ocurrence) 查找字符串的位置
第一个参数表示源字符串，第二个是要查找的字符，第三个是要查找的开始位置，第四个是查找的字符是第几个。
1.给某列前面增加字符：
UPDATE 表名 SET 列名=‘要添加的字符‘|| 列名
例如 substr((‘xx‘ || 字段名), 1, 8) 在字段前用‘||‘添加86,然后substr截取8位
2.给某列后面增加字符：
UPDATE 表名 SET 列名=列名||‘要添加的字符‘
//oracle 数据库
select nvl(t1.rscount, 0) as rscount,
字段
from (select count(0) as rscount, substr((‘86‘||字段),1,8) as 字段
from 表 a
where 字段 in
(select 字段 from 表 where 字段 like ‘xxx%‘)
and to_date(‘2018-09-01‘, ‘yyyy-mm-dd‘) <= a.CREATEDATE
and (to_date(‘2018-12-31‘, ‘yyyy-mm-dd‘) + 1) > a.CREATEDATE
group by 字段) t1,
(select 字段
from 表 b
where 字段 like ‘xxx%‘
and length(trim(b.字段)) = length(trim(‘xxx‘)) + 2
and b.ISACTIVE = 1
order by b.idx asc) t2
where t1.字段(+) = trim(t2.字段)
---- ////////////////////////////////////////////////////
select t1.rscount,t1.字段, t2.字段
from (select count(a.字段) as rscount,
TO_CHAR(CREATEDATE, ‘yyyy-mm‘) timevalue,
substr((‘xx‘||a.shiguid),1,8) as 字段
from 表 a
where 字段 in
(select trim(字段) from 表 where 字段 like ‘xxx%‘)
group by 字段,TO_CHAR(CREATEDATE, ‘yyyy-mm‘)) t1,
(select ‘2018-‘ || lpad(level, 2, 0) datevalue
from dual
connect by level < 13) t2
where t1.字段(+) = t2.字段 and (t1.字段=‘xxxxxx‘or t1.字段 is null)
order by t2.字段
///////////////////////////////////
oracle错误ora-01658的解决办法
此错误是报oracle的表空间大小不足。首先查看所有表空间的大小：
SELECT T.TABLESPACE_NAME, ROUND(SUM(BYTES/(1024 * 1024)), 0) TS_SIZE
FROM DBA_TABLESPACES T, DBA_DATA_FILES D
WHERE T.TABLESPACE_NAME = D.TABLESPACE_NAME
GROUP BY T.TABLESPACE_NAME;
然后查询要修改的表空间的数据文件名：
select file_name,blocks,tablespace_name
from dba_data_files
将对应表空间的dpf文件路径记下来。比如‘/opt/oracle/oradata/TEST/test.dbf’
最后修改表空间数据文件：
ALTER DATABASE DATAFILE ‘/opt/oracle/oradata/TEST/test.dbf‘ RESIZE 2000M;
////////////////////////////////////////////////tianjia
create table xt_dict as
select * From lrmdb_t.xt_dict
////////////////////////2018-12-18//////////////////////////////////////////////////////////
update 表 set 字段=(to_date((select 字段 from 表 t where 字段=‘xxxx‘),‘yyyy-mm-dd‘)+9) where 字段=‘201810121731362-D3862BAEF48F4EBFA12CCCC0BFFFF844‘
////////////////////////2018-12-20/////////////////////////////////
显然用to_date(time, ‘yyyy-mm-dd‘)直接转是不行的，得先用to_char(time, ‘yyyy-MM-dd‘)格式化一下。
最后变成这样to_date(to_char(time, ‘yyyy-MM-dd‘), ‘yyyy-mm-dd‘)，就不会报ORA-01861了。
//////////////////////////////////////////2019-1-16//////////////////
select * from 表 where 字段 in(select 字段 from 表 group by 字段 having count(字段)>1)
查找记录大于1的
///////////////////////////////////////////////////2019-1-17//////////////////
select top 20 * from WZ_GTYW except select top 13 * from WZ_GTYW where 查询指定行数
sql 替换字段中的部分字符，替换指定字符
把列中凡是有2011的全部修改成2014，如 lieming 里的201101131431改成201401131431，写法：
update tab set lieming = replace(lieming,‘2011‘,‘2014‘);
//////////////////////////////////////////////////2019-2-22//////////////////////////////////
https://www.cnblogs.com/cjm123/p/7940371.html sql 连接
select * from T_student s full join T_class c on s.classId = c.classId 全连接
//////////////////////////////////////////////////2019-03-08/////////////////////////////////////////////////////////////
Oracle中 如何用一个表的数据更新另一个表中的数据
merge into 表
using (select t.字段 ,max(t.字段) 字段 from 表 t group by t.字段)表
on (字段 = 字段)
when xxx then
update set 字段 = 字段
////////////////////////////////////////////////2019-3-20/////////////////////////////////////////////////////////////////////////
在SqlServer 中,,批量替换某个字段类型
-- 关闭 约束
declare tb cursor for
SELECT sql=‘alter table [‘+d.name+‘] NOCHECK CONSTRAINT all‘
FROM syscolumns a left join systypes b on a.xtype=b.xusertype
inner join sysobjects d on a.id=d.id and d.xtype=‘U‘ and d.name<>‘dtproperties‘
where b.name in(‘decimal‘) GROUP BY d.name
declare @sql1 varchar(1000)
open tb
fetch next from tb into @sql1
while @@fetch_status = 0
begin
print @sql1
exec(@SQL1)
fetch next from tb into @sql1
end
close tb
deallocate tb
-- 修改字段数据类型
declare Test1 cursor for
SELECT sql=‘alter table [‘+d.name+‘] alter column [‘+a.name+‘] int‘
FROM syscolumns a left join systypes b on a.xtype=b.xusertype
inner join sysobjects d on a.id=d.id and d.xtype=‘U‘ and d.name<>‘dtproperties‘
where b.name in(‘decimal‘) order by d.name,a.name
declare @sql2 varchar(1000)
open Test1
fetch next from Test1 into @sql2
while @@fetch_status = 0
begin
print @sql2
exec(@SQL2)
fetch next from Test1 into @sql2
end
close Test1
deallocate Test1
-- 恢复 约束
declare tb cursor for
SELECT sql=‘alter table [‘+d.name+‘] CHECK CONSTRAINT ALL‘
FROM syscolumns a left join systypes b on a.xtype=b.xusertype
inner join sysobjects d on a.id=d.id and d.xtype=‘U‘ and d.name<>‘dtproperties‘
where b.name in(‘decimal‘) GROUP BY d.name
declare @sql3 varchar(1000)
open tb
fetch next from tb into @sql3
while @@fetch_status = 0
begin
print @sql3
exec(@SQL3)
fetch next from tb into @sql3
end
close tb
deallocate tb
////////////////////////////////////////////////2019-03-28////////////////////////////////////////////////////////////////////////////
--SQL
--快速查看表结构
SELECT CASE WHEN col.colorder = 1 THEN obj.name
ELSE ‘‘
END AS 表名,
col.colorder AS 序号 ,
col.name AS 列名 ,
ISNULL(ep.[value], ‘‘) AS 列说明 ,
t.name AS 数据类型 ,
col.length AS 长度 ,
ISNULL(COLUMNPROPERTY(col.id, col.name, ‘Scale‘), 0) AS 小数位数 ,
CASE WHEN COLUMNPROPERTY(col.id, col.name, ‘IsIdentity‘) = 1 THEN ‘1‘
ELSE ‘‘
END AS 标识 ,
CASE WHEN EXISTS ( SELECT 1
FROM dbo.sysindexes si
INNER JOIN dbo.sysindexkeys sik ON si.id = sik.id
AND si.indid = sik.indid
INNER JOIN dbo.syscolumns sc ON sc.id = sik.id
AND sc.colid = sik.colid
INNER JOIN dbo.sysobjects so ON so.name = si.name
AND so.xtype = ‘PK‘
WHERE sc.id = col.id
AND sc.colid = col.colid ) THEN ‘1‘
ELSE ‘‘
END AS 主键 ,
CASE WHEN col.isnullable = 1 THEN ‘1‘
ELSE ‘‘
END AS 允许空 ,
ISNULL(comm.text, ‘‘) AS 默认值
FROM dbo.syscolumns col
LEFT JOIN dbo.systypes t ON col.xtype = t.xusertype
inner JOIN dbo.sysobjects obj ON col.id = obj.id
AND obj.xtype = ‘U‘
AND obj.status >= 0
LEFT JOIN dbo.syscomments comm ON col.cdefault = comm.id
LEFT JOIN sys.extended_properties ep ON col.id = ep.major_id
AND col.colid = ep.minor_id
AND ep.name = ‘MS_Description‘
LEFT JOIN sys.extended_properties epTwo ON obj.id = epTwo.major_id
AND epTwo.minor_id = 0
AND epTwo.name = ‘MS_Description‘
WHERE obj.name = ‘XS‘--表名
ORDER BY col.colorder ;
//////////////////////////////////////////////////2019-03-28///////////////////////////////////////////////////////////////////////////////
sql 排序
select * from (select ROW_NUMBER()over(order by id desc) as rowNum, * from (SQL 语句) as Y) as t where rowNum>10 and rowNum<=20
SELECT TOP 10 * from (SELECT ROW_NUMBER() OVER (ORDER BY ID desc) AS RowNumber,* FROM ( sql 语句 或者表名)AS B) as A where rownumber>10
////////////////////////////////////////////////////2019-04-17///////////////////////////////////////////////////////////////////////////////
str = str.Replace("‘", "");
str = str.Replace("<", "");
str = str.Replace(">", "");
str = str.Replace("%", "");
str = str.Replace("‘delete", "");
str = str.Replace("‘‘", "");
str = str.Replace("""", "");
str = str.Replace(",", "");
str = str.Replace(".", "");
str = str.Replace(">=", "");
str = str.Replace("=<", "");
str = str.Replace("-", "");
str = str.Replace("_", "");
str = str.Replace(";", "");
str = str.Replace("||", "");
str = str.Replace("[", "");
str = str.Replace("]", "");
str = str.Replace("&", "");
str = str.Replace("#", "");
str = str.Replace("/", "");
str = str.Replace("-", "");
str = str.Replace("|", "");
str = str.Replace("?", "");
str = str.Replace(">?", "");
str = str.Replace("?<", "");
str = str.Replace(" ", "");
/////////////////////////////////////////////////////20190509////////////////////////////////////////////////////////////////////////////////////
System.ServiceProcess.ServiceController sc = new System.ServiceProcess.ServiceController("TLKJ_TASK_CLIENT");
if (sc.Status == System.ServiceProcess.ServiceControllerStatus.Running)
{
log4net.WriteLogFile("准备关闭服务", 55);
sc.Stop();
sc.WaitForStatus(System.ServiceProcess.ServiceControllerStatus.Stopped); //等待服务停止
if (sc.Status == System.ServiceProcess.ServiceControllerStatus.Stopped)
{
sc.Start();
log4net.WriteLogFile("成功开启服务",55);
}
}
/////////////////////////////////////////////////////20190524/////////////////////////////////////////////////////////////////////////////////////////////
sql server 查询数据结构
SELECT
表名 = Case When A.colorder=1 Then D.name Else ‘‘ End,
表说明 = Case When A.colorder=1 Then isnull(F.value,‘‘) Else ‘‘ End,
字段序号 = A.colorder,
字段名 = A.name,
字段说明 = isnull(G.[value],‘‘),
标识 = Case When COLUMNPROPERTY( A.id,A.name,‘IsIdentity‘)=1 Then ‘√‘Else ‘‘ End,
主键 = Case When exists(SELECT 1 FROM sysobjects Where xtype=‘PK‘ and parent_obj=A.id and name in (
SELECT name FROM sysindexes WHERE indid in( SELECT indid FROM sysindexkeys WHERE id = A.id AND colid=A.colid))) then ‘√‘ else ‘‘ end,
类型 = B.name,
占用字节数 = A.Length,
长度 = COLUMNPROPERTY(A.id,A.name,‘PRECISION‘),
小数位数 = isnull(COLUMNPROPERTY(A.id,A.name,‘Scale‘),0),
允许空 = Case When A.isnullable=1 Then ‘√‘Else ‘‘ End,
默认值 = isnull(E.Text,‘‘)
FROM
syscolumns A
Left Join
systypes B
On
A.xusertype=B.xusertype
Inner Join
sysobjects D
On
A.id=D.id and D.xtype=‘U‘ and D.name<>‘dtproperties‘
Left Join
syscomments E
on
A.cdefault=E.id
Left Join
sys.extended_properties G
on
A.id=G.major_id and A.colid=G.minor_id
Left Join
sys.extended_properties F
On
D.id=F.major_id and F.minor_id=0
--where d.name=‘OrderInfo‘ --如果只查询指定表,加上此条件
Order By
A.id,A.colorder
/////////sql server 数据结构导出成html
Set nocount on
DECLARE @TableName nvarchar(35)
DECLARE Tbls CURSOR
FOR
Select distinct Table_name
FROM INFORMATION_SCHEMA.COLUMNS
--put any exclusions here
--where table_name not like ‘%old‘
order by Table_name
OPEN Tbls
PRINT ‘<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">‘
PRINT ‘<html xmlns="http://www.w3.org/1999/xhtml">‘
PRINT ‘<head>‘
PRINT ‘<title>数据库字典</title>‘
PRINT ‘<style type="text/css">‘
PRINT ‘body{margin:0; font:11pt "arial", "微软雅黑"; cursor:default;}‘
PRINT ‘.tableBox{margin:10px auto; padding:0px; width:1200px; height:auto; background:#FBF5E3; border:1px solid #45360A}‘
PRINT ‘.tableBox h3 {font-size:12pt; min-height:30px; line-height:30px; background:#45360A; padding:0px 0px 0px 15px; color:#FFF; margin:0px; text-align:left }‘
PRINT ‘.tableBox table {width:1200px; padding:0px }‘
PRINT ‘.tableBox th {height:25px; border-top:1px solid #FFF; border-left:1px solid #FFF; background:#F7EBC8; border-right:1px solid #E0C8; border-bottom:1px solid #E0C8 }‘
PRINT ‘.tableBox td {height:25px; padding-left:10px; border-top:1px solid #FFF; border-left:1px solid #FFF; border-right:1px solid #E0C8; border-bottom:1px solid #E0C8 }‘
PRINT ‘</style>‘
PRINT ‘</head>‘
PRINT ‘<body>‘
FETCH NEXT FROM Tbls
INTO @TableName
WHILE @@FETCH_STATUS = 0
BEGIN
PRINT ‘<div class="tableBox">‘
--表说明齐全时候 可以用这个
-- Select ‘<h3>表‘ + @TableName +
--‘ : ‘+cast(Value as varchar(1000)) +
-- ‘</h3>‘
-- FROM sys.extended_properties A
-- WHERE A.major_id = OBJECT_ID(@TableName)
-- and name = ‘MS_Description‘
-- and minor_id = 0
--表说明不齐全的时候
print ‘<h3>表‘ + @TableName+‘ : ‘
select ISNULL(cast((select a.value
FROM sys.extended_properties A
WHERE A.major_id = OBJECT_ID( @TableName)
and name = ‘MS_Description‘
and minor_id = 0) as nvarchar(100)),‘‘)
print ‘</h3>‘
PRINT ‘<table cellspacing="0">‘
--Get the Description of the table
--Characters 1-250
PRINT ‘<tr>‘ --Set up the Column Headers for the Table
PRINT ‘<th>字段名称</th>‘
PRINT ‘<th>描述</th>‘
PRINT ‘<th>主键</th>‘
PRINT ‘<th>外键</th>‘
PRINT ‘<th>类型</th>‘
PRINT ‘<th>长度</th>‘
PRINT ‘<th>数值精度</th>‘
PRINT ‘<th>小数位数</th>‘
PRINT ‘<th>允许为空</th>‘
PRINT ‘<th>计算列</th>‘
PRINT ‘<th>标识列</th>‘
PRINT ‘<th>默认值</th>‘
--Get the Table Data
SELECT ‘</tr><tr>‘,
‘<td>‘ + CAST(clmns.name AS VARCHAR(60)) + ‘</td>‘,
‘<td>‘ + ISNULL(CAST(exprop.value AS VARCHAR(500)),‘‘) + ‘</td>‘,
‘<td>‘ + CAST(ISNULL(idxcol.index_column_id, 0)AS VARCHAR(60)) + ‘</td>‘,
‘<td>‘ + CAST(ISNULL(
(SELECT TOP 1 1
FROM sys.foreign_key_columns AS fkclmn
WHERE fkclmn.parent_column_id = clmns.column_id
AND fkclmn.parent_object_id = clmns.object_id
), 0) AS VARCHAR(20)) + ‘</td>‘,
‘<td>‘ + CAST(udt.name AS CHAR(15)) + ‘</td>‘ ,
‘<td>‘ + CAST(CAST(CASE WHEN typ.name IN (N‘nchar‘,N‘varchar‘, N‘nvarchar‘) AND clmns.max_length <> -1
THEN clmns.max_length/2
ELSE clmns.max_length END AS INT) AS VARCHAR(20)) + ‘</td>‘,
‘<td>‘ + CAST(CAST(clmns.precision AS INT) AS VARCHAR(20)) + ‘</td>‘,
‘<td>‘ + CAST(CAST(clmns.scale AS INT) AS VARCHAR(20)) + ‘</td>‘,
‘<td>‘ + CAST(clmns.is_nullable AS VARCHAR(20)) + ‘</td>‘ ,
‘<td>‘ + CAST(clmns.is_computed AS VARCHAR(20)) + ‘</td>‘ ,
‘<td>‘ + CAST(clmns.is_identity AS VARCHAR(20)) + ‘</td>‘ ,
‘<td>‘ + isnull(CAST(cnstr.definition AS VARCHAR(20)),‘‘) + ‘</td>‘
FROM sys.tables AS tbl INNER JOIN sys.all_columns AS clmns
ON clmns.object_id=tbl.object_id
LEFT OUTER JOIN sys.indexes AS idx
ON idx.object_id = clmns.object_id
AND 1 =idx.is_primary_key
LEFT OUTER JOIN sys.index_columns AS idxcol
ON idxcol.index_id = idx.index_id
AND idxcol.column_id = clmns.column_id
AND idxcol.object_id = clmns.object_id
AND 0 = idxcol.is_included_column
LEFT OUTER JOIN sys.types AS udt
ON udt.user_type_id = clmns.user_type_id
LEFT OUTER JOIN sys.types AS typ
ON typ.user_type_id = clmns.system_type_id
AND typ.user_type_id = typ.system_type_id
LEFT JOIN sys.default_constraints AS cnstr
ON cnstr.object_id=clmns.default_object_id
LEFT OUTER JOIN sys.extended_properties exprop
ON exprop.major_id = clmns.object_id
AND exprop.minor_id = clmns.column_id
-- AND exprop.name = ‘MS_Description‘
WHERE (tbl.name = @TableName
--and exprop.class = 1 --这个是表注说明不可为空
) --I don‘t wand to include comments on indexes
ORDER BY clmns.column_id ASC
PRINT ‘</tr></table>‘
PRINT ‘</div>‘
FETCH NEXT FROM Tbls
INTO @TableName
END
PRINT ‘</body></HTML>‘
CLOSE Tbls
DEALLOCATE Tbls
///oracle 查询表结构
SELECT t1.Table_Name || chr(13) || t3.comments AS "表名称及说明",
--t3.comments AS "表说明",
t1.Column_Name AS "字段名称",
t1.DATA_TYPE || ‘(‘ || t1.DATA_LENGTH || ‘)‘ AS "数据类型",
t1.NullAble AS "是否为空",
t2.Comments AS "字段说明",
t1.Data_Default "默认值"
--t4.created AS "建表时间"
FROM cols t1
LEFT JOIN user_col_comments t2
ON t1.Table_name = t2.Table_name
AND t1.Column_Name = t2.Column_Name
LEFT JOIN user_tab_comments t3
ON t1.Table_name = t3.Table_name
LEFT JOIN user_objects t4
ON t1.table_name = t4.OBJECT_NAME
WHERE NOT EXISTS (SELECT t4.Object_Name
FROM User_objects t4
WHERE t4.Object_Type = ‘TABLE‘
AND t4.Temporary = ‘Y‘
AND t4.Object_Name = t1.Table_Name)
ORDER BY t1.Table_Name, t1.Column_ID;
///mysql 数据字典 配合Navicat Premium 12 用
select
c.TABLE_SCHEMA as ‘数据库‘,
c.TABLE_NAME as ‘表名‘,
c.COLUMN_NAME as ‘字段名称‘,
c.COLUMN_COMMENT as ‘字段描述‘,
c.COLUMN_TYPE as ‘数据类型 ‘,
IF(kcu.ORDINAL_POSITION is not NULL,‘√‘,‘ ‘ ) AS ‘主键‘,
IF(c.IS_NULLABLE=‘YES‘,‘√‘,‘ ‘ ) AS ‘为空‘,
COLUMN_COMMENT as ‘取值说明‘
from information_schema.columns c
left join information_schema.key_column_usage kcu
on kcu.TABLE_SCHEMA=‘mysql‘ --这个写数据库名
and c.TABLE_NAME = kcu.TABLE_NAME and c.COLUMN_NAME = kcu.COLUMN_NAME
where c.TABLE_SCHEMA=‘mysql‘ --这个写数据库名
//////////////////////////////////////////////////////20190604//////////////////////////////////////////////////////////////////
oracle id 自增设置
1.设置序列
-- Create sequence
create sequence IDS7
minvalue 1
maxvalue 999999999999999999999999999
start with 1681131
increment by 1
cache 20;
2.设置函数
-- 获取序列下一个值
create or replace function get_seq_next (seq_name in varchar2) return number
is
seq_val number ;
begin
execute immediate ‘select ‘|| seq_name|| ‘.nextval from dual‘ into seq_val ;
return seq_val ;
end get_seq_next;
3.调用
select get_seq_next(‘ids7‘) from dual;
//////////////////////////////////////////////////20190628*////////////////////////////////////////////////////////////////////////
select ‘男‘=(select count(t.Age) from SysUser t where t.Age=1),‘女‘=(select count(a.Age) from SysUser a where a.Age=0) ; 两个查询结果放在一行；
select ep_classes, ep_name = (stuff((select ‘,‘ + ep_name from ep_detail where ep_classes =
a.ep_classes for xml path(‘‘)),1,1,‘‘)) from ep_detail a group by ep_classes; 具有相同ep_classes 不同ep_name 查询结果放在一行
oracle 使用 select wm_concat(要查询内容) from test
写sql语句时候遇到的一些问题
标签：creat ret group by doctype full join 解决 media varchar2 string
热心网友
时间：2022-05-03 04:02
是多表查询，其中两个以上的表有同名的字段，在语句中没指明哪个表。
所以是unknowncolumn，SQL不知道是哪个表的字段。
在检查SQL语句完全无误后，可以检查下表中的数据类型设置或者字符编码格式，比如在出现这个错误时，常常因为数据库使用的是gbk格式，但是字段是utf8编码格式的，表中字段编码格式不同，导致了这个错误。
扩展资料：
SQL是操作数据库数据的结构化查询语言，网页的应用数据和后台数据库中的数据进行交互时会采用SQL。而SQL注入是将Web页面的原URL、表单域或数据包输入的参数，修改拼接成SQL语句，传递给Web服务器，进而传给数据库服务器以执行数据库命令。
如Web应用程序的开发人员对用户所输入的数据或cookie等内容不进行过滤或验证(即存在注入点)就直接传输给数据库，就可能导致拼接的SQL被执行，获取对数据库的信息以及提权，发生SQL注入攻击。
参考资料来源：百度百科-sql注入
热心网友
时间：2022-05-03 05:20
写sql语句时语句里面没有空格或多了空格导致的。
如写sql的时候正常是这样：
"select student_id,student_name,student_age,student_gender from student";
如果你在idea里sql语句有换行：
"select student_id,student_name,student_age,student_gender" +
"from student";
写成这样是不对的，会导致gender和from之间没有了空格，误认为一块了。正确写法是在gender后面或者from前面加一个空格：
"select student_id,student_name,student_age,student_gender " +
"from student";
热心网友
时间：2022-05-03 06:55
应该是多表查询，其中两个以上的表有同名的字段，在语句中没指明哪个表。
所以是unknown column，SQL不知道是哪个表的字段。追问原来是字段多了一个空格。
热心网友
时间：2022-05-03 08:46
我也遇到了这个问题，已经解决了。
假设你是从3张表中取数据列（这些数据列分散在三张表中，表之间通过这些数据连接），而你select时只打印其中一部分数据（这部分需打印的数据只在3张表中的某2张之中），那么第三张表也必须在from子句中说明，不然就会提示unknow column
热心网友
时间：2022-05-03 10:54
如果单表查询 那有可能是 列的字段名前面有空格 可以检查下
热心网友
时间：2022-05-03 13:19
贴上来看看。
热心网友
时间：2022-05-03 16:00
表结构和sql贴点出来才好看呢
