请参阅本说明末尾的重要新发现 1 和 2。
我正在运行 Postgres 9.1.3 并且遇到了一个奇怪的左连接问题。
我有一个名为consistent.master的表,其中包含超过200 万行。它有一个名为citation_id的列,并且该列没有空值。我可以用这个来验证:
SELECT COUNT(*)
FROM consistent.master
WHERE citation_id IS NULL
那返回0。
这就是奇怪的地方:如果我将此表LEFT JOIN 加入临时表,我会收到一个错误,我试图在citation_id字段中插入一个空值:
错误:“citation_id”列中的空值违反非空约束 SQL 状态:23502
这是查询:
WITH stops AS (
SELECT citation_id,
rank() OVER (ORDER BY offense_timestamp,
defendant_dl,
offense_street_number,
offense_street_name) AS stop
FROM consistent.master
WHERE citing_jurisdiction=1
)
INSERT INTO consistent.masternew (arrest_id, citation_id, defendant_dl, defendant_dl_state, defendant_zip, defendant_race, defendant_sex, defendant_dob, vehicle_licenseplate, vehicle_licenseplate_state, vehicle_registration_expiration_date, vehicle_year, vehicle_make, vehicle_model, vehicle_color, offense_timestamp, offense_street_number, offense_street_name, offense_crossstreet_number, offense_crossstreet_name, offense_county, officer_id, offense_code, speed_alleged, speed_limit, work_zone, school_zone, offense_location, id, source, citing_jurisdiction, the_geom)
SELECT stops.stop, master.citation_id, defendant_dl, defendant_dl_state, defendant_zip, defendant_race, defendant_sex, defendant_dob, vehicle_licenseplate, vehicle_licenseplate_state, vehicle_registration_expiration_date, vehicle_year, vehicle_make, vehicle_model, vehicle_color, offense_timestamp, offense_street_number, offense_street_name, offense_crossstreet_number, offense_crossstreet_name, offense_county, officer_id, offense_code, speed_alleged, speed_limit, work_zone, school_zone, offense_location, id, source, citing_jurisdiction, the_geom
FROM consistent.master LEFT JOIN stops
ON stops.citation_id = master.citation_id
我在这个问题上摸不着头脑。如果这是一个LEFT JOIN,并且如果一致.master是连接的左表,那么这个查询如何在没有任何开头的citation_id列中创建空值?
这是我用来创建表的 SQL 代码:
CREATE TABLE consistent.masternew
(
arrest_id character varying(20),
citation_id character varying(20) NOT NULL,
defendant_dl character varying(20),
defendant_dl_state character varying(2),
defendant_zip character varying(9),
defendant_race character varying(10),
defendant_sex character(1),
defendant_dob date,
vehicle_licenseplate character varying(10),
vehicle_licenseplate_state character(2),
vehicle_registration_expiration_date date,
vehicle_year integer,
vehicle_make character varying(20),
vehicle_model character varying(20),
vehicle_color character varying,
offense_timestamp timestamp without time zone,
offense_street_number character varying(10),
offense_street_name character varying(30),
offense_crossstreet_number character varying(10),
offense_crossstreet_name character varying(30),
offense_county character varying(10),
officer_id character varying(20),
offense_code integer,
speed_alleged integer,
speed_limit integer,
work_zone bit(1),
school_zone bit(1),
offense_location point,
id serial NOT NULL,
source character varying(20), -- Where this citation came from--court, PD, etc.
citing_jurisdiction integer,
the_geom geometry,
CONSTRAINT masternew_pkey PRIMARY KEY (id ),
CONSTRAINT citing_jurisdiction FOREIGN KEY (citing_jurisdiction)
REFERENCES consistent.jurisdictions (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT offenses FOREIGN KEY (offense_code)
REFERENCES consistent.offenses (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT enforce_dims_the_geom CHECK (st_ndims(the_geom) = 2),
CONSTRAINT enforce_geotype_the_geom CHECK (geometrytype(the_geom) = 'POINT'::text OR the_geom IS NULL),
CONSTRAINT enforce_srid_the_geom CHECK (st_srid(the_geom) = 3081)
)
WITH (
OIDS=FALSE
);
ALTER TABLE consistent.masternew
OWNER TO postgres;
COMMENT ON COLUMN consistent.masternew.source IS 'Where this citation came from--court, PD, etc.';
CREATE INDEX masternew_citation_id_idx
ON consistent.masternew
USING btree
(citation_id COLLATE pg_catalog."default" );
CREATE INDEX masternew_citing_jurisdiction_idx
ON consistent.masternew
USING btree
(citing_jurisdiction );
CREATE INDEX masternew_defendant_dl_idx
ON consistent.masternew
USING btree
(defendant_dl COLLATE pg_catalog."default" );
CREATE INDEX masternew_id_idx
ON consistent.masternew
USING btree
(id );
CREATE INDEX masternew_offense_street_name_idx
ON consistent.masternew
USING btree
(offense_street_name COLLATE pg_catalog."default" );
CREATE INDEX masternew_offense_street_number_idx
ON consistent.masternew
USING btree
(offense_street_number COLLATE pg_catalog."default" );
CREATE INDEX masternew_offense_timestamp_idx
ON consistent.masternew
USING btree
(offense_timestamp );
CREATE INDEX masternew_the_geom_idx
ON consistent.masternew
USING gist
(the_geom );
重要发现 1
我刚刚发现了一些有趣的事情。这个查询:
SELECT COUNT(*)
FROM consistent.master
WHERE citation_id IS NOT NULL
UNION
SELECT COUNT(*)
FROM consistent.master
UNION
SELECT COUNT(*)
FROM consistent.master
WHERE citation_id IS NULL
结果是:
2085344
2085343
0
我怎么可能解释呢?计数如何WHERE citation_id IS NOT NULL
可能高于没有WHERE
子句的相同查询?
重要发现 2
好的,根据下面的评论,我发现我有一行包含所有空值,尽管该表有一个串行id
列和一些NOT NULL
约束。
我删除了流浪汉行。现在我没有收到空错误。相反,我得到了这个:
ERROR: duplicate key value violates unique constraint "masternew_pkey"
DETAIL: Key (id)=(1583804) already exists.
********** Error **********
ERROR: duplicate key value violates unique constraint "masternew_pkey"
SQL state: 23505
Detail: Key (id)=(1583804) already exists.
所以为了确保,我做这个查询:
SELECT COUNT(id)
FROM consistent.master
WHERE id=1583804;
你猜怎么了?consistent.master
只有 1 个这样的实例!所以考虑到左表LEFT JOIN
只有1个1583804的实例,citation_id
并且id列只能来自左表,怎么可能发生这个错误呢?这样的LEFT JOIN
结果不应该导致最终结果的行数比左表多,对吧?