您可以使用多态表函数执行此任务。但是，要求并不明确，因为您可以在构建SQL查询时指定所需的列：应用程...
这个做不到的，因为你在别的表里面动态查出来的是个字符串，放在这里相当于是个常量 可以使用动态sql试试 select X into v_col from table2;execute immediate 'select '||v_col||' from table1';
Oracle SELECT examples Let’s take some examples of using the OracleSELECTstatement to understand how it works. A) query data from a single column To get the customer names from thecustomerstable, you use the following statement: SELECTnameFROMcustomers;Code language:SQL (Structured Query Language...
SQL1:select decode(t.num_rows, 0, t.table_name, null) 无数据的表,decode(t.num_rows, 0, null, t.table_name) 有数据的表 from user_tables t where t.table_name in (SELECT t1.table_name FROM All_All_Tables t1);SQL2 select decode(t.num_rows, 0, t.table_name, null)...
table表是一个数据表，假设表的行数为10行。1：select 1 from table 增加临时列，每行的列值是写在select后的数，这条sql语句中是1 2：select count(1) from table 不管count(a)的a值如何变化，得出的值总是table表的行数 3：select sum(1) from table 计算临时列的和 在SQL ...
Oracle中select count(*) from table是统计表的行数。如：select count(*) from emp;查询结果：其中查询结果中的15代表emp表中共有15行记录。
SELECT *|{[DISTINCT] column|expression [alias],...} FROM table [WHERE condition(s)] [order by column|expression| alias ]; Where 一定要放在FROM 子句的后面。 显示表的部分行和部分列,使用where子句过滤出想要的行 Select deptno,ename from emp Where deptno=10; ...
Oracle - SELECT 1 FROM table; SELECT COUNT(1) FROM table; SELECT 1 SELECT1FROMtableSELECTanyColumnFROMtableSELECT*FROMtable 效率上:1 > anyColumn > * 因为 SELECT 1 不用查字典。 SELECT1, r.mcFROMry rWHEREROWNUM<=10 SELECT 1 给查询的记录加一个临时列。查看是否有记录,一般作为查询条件使用。
SELECT columna columnb FROM mytable; For this reason, it is good practice to be in the habit of using AS explicitly when specifying column aliases. It is not permissible to refer to a column alias in a WHERE clause, because the column value might not yet be determined when the WHERE...
The c_alias list following the CYCLE keyword must contain column names from the column alias list for query_name. Oracle Database uses these columns to detect a cycle. cycle_value and no_cycle_value should be character strings of length 1. If a cycle is detected, then the cycle mark ...