Teradata TD Varchar會比char省空間嗎?
CHAR(n)固定是用掉n Bytes(LATIN; UNICODE則是2倍) VARCHAR每個字元用掉n Bytes，另外再加2Bytes放長度資訊。 所以，資料是NULL，在 CHAR(10) => 10 BYTES VARCHAR(10) => 0+2 BYTES 選用規則：視資料內容變動性來決定，如果資料平均變動(少於 N的長度)大於3，則選用VARCHAR在空間上就有節省的空間。 例如：要用CHAR(10) 或是VARCHAR(10)? 看資料平均長度是小於等於7，選VARCHAR(10)就可以省空間。 若有一定的資料是NULL，也可以考慮用CHAR(n) COMPRESS，把NULL壓起來。 VARCHAR(1)、VARCHAR(2)在空間上絕對是不合適的定義。 https://downloads.teradata.com/forum/database/recommendation-on-varhar-char-columns CHAR(n) always need exactly n bytes for LATIN or n*2 bytes for UNICODE while VARCHARs need 1 or two bytes for each character stored. But VARCHARs also need two byte additional overhead (a word indicating the length). Assuming your columns are mainly Y/N or similar in LATIN a single character needs 3 bytes as a VARCHAR, but only 1 byte as CHAR. You never ever do a VARCHAR(1) on Teradata :-) When the actual length of a string greatly varies and the average is at least 3 characters than the maximum you start using VARCHARS. Q2: FastLoad calculates the n...
