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TEXT | text | ûÓÐÌØ±ðµÄÉÏÏÞÏÞÖÆ£¨½öÊÜÐеÄ×î´ó³¤¶ÈÏÞÖÆ£© |
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BYTEA | bytea | ±ä³¤×Ö½ÚÐòÁУ¨Ê¹ÓÃNULLÒ²ÊÇÔÊÐíµÄ£© |
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"char" | char | Ò»¸ö×Ö·û |
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+ ÓÚÊÇʵ¼ÊÕ¼ÓõĿռä±ÈÉùÃ÷µÄ´óСҪ¶àһЩ¡£
+ È»¶øÕâЩÀàÐͶ¼¿ÉÒÔ±»Ñ¹Ëõ´æ´¢£¬Ò²¿ÉÒÔÓà TOAST ÍÑ»ú´æ´¢£¬Òò´Ë´ÅÅ̿ռäÒ²¿ÉÄܱÈÔ¤ÏëµÄÒªÉÙ¡£
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+ VARCHAR(n) ÔÚ´æ´¢ÏÞÖÆÁË×î´ó³¤¶ÈµÄ±ä³¤×Ö·û´®ÊÇ×îºÃµÄ¡£
+ TEXT ÊÊÓÃÓÚ´æ´¢×î´ó¿É´ï 1G×óÓÒµ«Î´¶¨ÒåÏÞÖÆ³¤¶ÈµÄ×Ö·û´®¡£
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+ CHAR(n) ×îÊʺÏÓÚ´æ´¢³¤¶ÈÏàͬµÄ×Ö·û´®¡£ CHAR(n)»á¸ù¾ÝËù¸ø¶¨µÄ×ֶ㤶ÈÒÔ¿Õ¸ñ²¹×㣨²»×ãµÄ×Ö¶ÎÄÚÈÝ£©£¬
+ ¶ø VARCHAR(n) Ö»´æ´¢Ëù¸ø¶¨µÄÊý¾ÝÄÚÈÝ¡£
+ BYTEA ÓÃÓÚ´æ´¢¶þ½øÖÆÊý¾Ý£¬ÓÈÆäÊǰüº¬ NULL ×Ö½ÚµÄÖµ¡£ÕâЩÀàÐ;ßÓÐÏàËÆµÄÐÔÄÜÌØÐÔ¡£
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4.11.1)ÎÒÔõÑù´´½¨Ò»¸öÐòÁкÅ/×Ô¶¯µÝÔöµÄ×ֶΣ¿
+ PostgreSQL Ö§³Ö SERIAL Êý¾ÝÀàÐÍ¡£ËüÔÚ×Ö¶ÎÉÏ×Ô¶¯´´½¨Ò»¸öÐòÁкÍË÷Òý¡£ÀýÈ磺
+
+ CREATE TABLE person (
+ id SERIAL,
+ name TEXT
+ );
+
+ »á×Ô¶¯×ª»»Îª£º
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+ CREATE SEQUENCE person_id_seq;
+ CREATE TABLE person (
+ id INT4 NOT NULL DEFAULT nextval('person_id_seq'),
+ name TEXT
+ );
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+ ²Î¿¼ create_sequence ÊÖ²áÒ³»ñÈ¡¹ØÓÚÐòÁеĸü¶àÐÅÏ¢¡£
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+ Ò»ÖÖ·½·¨ÊÇÔÚ²åÈë֮ǰÏÈÓú¯Êý nextval() ´ÓÐòÁжÔÏóÀï¼ìË÷³öÏÂÒ»¸ö SERIAL Öµ£¬È»ºóÔÙÏÔʽ²åÈ롣ʹÓÃ
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4.11.1 ÀïµÄÀý±í£¬¿ÉÓÃαÂëÕâÑùÃèÊö£º
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+ new_id = execute("SELECT nextval('person_id_seq')");
+ execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')");
+
+ ÕâÑù»¹ÄÜÔÚÆäËû²éѯÖÐʹÓôæ·ÅÔÚ new_id ÀïµÄÐÂÖµ£¨ÀýÈ磬×÷Ϊ person ±íµÄÍâ¼ü£©¡£
+ ×¢Òâ×Ô¶¯´´½¨µÄ SEQUENCE ¶ÔÏóµÄÃû³Æ½«»áÊÇ <table>_<serialcolumn>_seq£¬
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+
+ execute("INSERT INTO person (name) VALUES ('Blaise Pascal')");
+ new_id = execute("SELECT currval('person_id_seq')");
+
+
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4.11.3)ʹÓà currval() »áµ¼ÖÂºÍÆäËûÓû§µÄ³åÍ»Çé¿ö£¨race condition£©Âð£¿
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4.13)ΪʲôÎÒÊÕµ½´íÎóÐÅÏ¢¡°ERROR: Memory exhausted in AllocSetAlloc()¡±£¿
+ ÕâºÜ¿ÉÄÜÊÇϵͳµÄÐéÄâÄÚ´æÓùâÁË£¬»òÕßÄں˶ÔijЩ×ÊÔ´Óнϵ͵ÄÏÞÖÆÖµ¡£ÔÚÆô¶¯ postmaster ֮ǰÊÔÊÔÏÂÃæµÄÃüÁ
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+ ulimit -d 262144
+ limit datasize 256m
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+ ´Ó psql ÀÊäÈë SELECT version();
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+ ʹÓà CURRENT_TIMESTAMP£º
+
+ CREATE TABLE test (x int, modtime TIMESTAMP DEFAULT CURRENT_TIMESTAMP );
+
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+
+ SELECT *
+ FROM t1 LEFT OUTER JOIN t2 ON (t1.col = t2.col);
+
+ SELECT *
+ FROM t1 LEFT OUTER JOIN t2 USING (col);
+
+ ÕâÁ½¸öµÈ¼ÛµÄ²éѯÔÚ t1.col ºÍ t2.col ÉÏ×öÁ¬½Ó£¬²¢ÇÒ·µ»Ø t1 ÖÐËùÓÐδÁ¬½ÓµÄÐУ¨ÄÇЩÔÚ t2 ÖÐûÓÐÆ¥ÅäµÄÐУ©¡£
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