oracle字符连接

oracle 使用||连接字符时原来的尾部空格不会被忽略，如

CREATE TABLE tab1 (col1 VARCHAR2(6), col2 CHAR(6),
        col3 VARCHAR2(6), col4 CHAR(6) );

INSERT INTO tab1 (col1,  col2,     col3,     col4)
        VALUES   ('abc', 'def   ', 'ghi   ', 'jkl');

SELECT col1||col2||col3||col4 "Concatenation"
        FROM tab1;

Concatenation
------------------------
abcdef   ghi   jkl

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