3.3    “：：”数据转换PostgreSQL 数据之间的转换可以使用“：：”操作符。3.3.1   text to varcharvperson 表gender字段为布尔型（boolean）在视图中要显示为true显示为“先生”，false显示为“女士”CASE WHEN 表达式应该是：CASE WHEN p.gender = true THEN '先生' ELSE '女士' END as gender,直接使用'先生', '女士' PostgreSQL认为' '中间的字符为text类型，请看下面：postgres=# CREATE OR REPLACE VIEW vperson ASpostgres-#     SELECT p.uid,p.name,postgres-#     CASE WHEN p.gender = true THEN '先生' ELSE '女士' END as gender,postgres-#     p.nickname,p.mobile,p.tel,p.fax,p.email,p.province,p.city,p.address,p.postalcodepostgres-#     FROM "person" ppostgres-#     Order By p.uid;CREATE VIEWpostgres=# \dv vperson         List of relations Schema |  Name   | Type |  Owner--------+---------+------+---------- public | vperson | view | postgres(1 row)postgres=# \d person                    Table "public.person"   Column    |          Type          |      Modifiers-------------+------------------------+---------------------- uid         | integer                | not null default 0 name        | character varying(20)  | not null gender      | boolean                | not null default 'F' nickname    | character varying(20)  | mobile      | character varying(13)  | tel         | character varying(20)  | not null fax         | character varying(20)  | email       | character varying(60)  | province    | character varying(10)  | not null city        | character varying(10)  | not null address     | character varying(255) | not null postalcode  | character varying(6)   | not null rate        | character varying(20)  | default '0' bank        | character varying(20)  | not null default '' bankaccount | character varying(20)  | not null default ''Indexes: person_pkey primary key btree (uid)Check constraints: "person_rate" ((((((rate = '0'::character varying) OR (rate = '1'::character varying)) OR (rate = '2'::character varying)) OR (rate = '3'::character varying)) OR (rate = '4'::character varying)) OR (rate = '5'::character varying))postgres=#postgres=# \d vperson              View "public.vperson"   Column   |          Type          | Modifiers------------+------------------------+----------- uid        | integer                | name       | character varying(20)  | gender     | text                   | nickname   | character varying(20)  | mobile     | character varying(13)  | tel        | character varying(20)  | fax        | character varying(20)  | email      | character varying(60)  | province   | character varying(10)  | city       | character varying(10)  | address    | character varying(255) | postalcode | character varying(6)   |View definition: SELECT p.uid, p.name, CASE WHEN (p.gender = true) THEN '先生'::text ELSE '女士'::text END AS gender, p.nickname, p.mobile, p.tel, p.fax, p.email, p.province, p.city, p.address, p.postalcode FROM person p ORDER BY p.uid;使用“：：”将test 转为varchar：CASE WHEN p.gender = true THEN '先生'::varchar(2) ELSE '女士'::varchar(2) END as gender,例：CREATE OR REPLACE VIEW vperson AS    SELECT p.uid,p.name,           CASE WHEN p.gender = true THEN '先生'::varchar(2) ELSE '女士'::varchar(2) END as gender,           p.nickname,p.mobile,p.tel,p.fax,p.email,p.province,p.city,p.address,p.postalcode    FROM "person" p    Order By p.uid;postgres=# drop view vperson ;DROP VIEWpostgres=# CREATE OR REPLACE VIEW vperson ASpostgres-#     SELECT p.uid,p.name,postgres-#     CASE WHEN p.gender = true THEN '先生'::varchar(2) ELSE '女士'::varchar(2) END as gender,postgres-#     p.nickname,p.mobile,p.tel,p.fax,p.email,p.province,p.city,p.address,p.postalcodepostgres-#     FROM "person" ppostgres-#     Order By p.uid;CREATE VIEWpostgres=# \d vperson              View "public.vperson"   Column   |          Type          | Modifiers------------+------------------------+----------- uid        | integer                | name       | character varying(20)  | gender     | character varying(2)   | nickname   | character varying(20)  | mobile     | character varying(13)  | tel        | character varying(20)  | fax        | character varying(20)  | email      | character varying(60)  | province   | character varying(10)  | city       | character varying(10)  | address    | character varying(255) | postalcode | character varying(6)   |View definition: SELECT p.uid, p.name, CASE WHEN (p.gender = true) THEN ('先生'::character varying)::character varying(2) ELSE ('女士'::character varying)::character varying(2) END AS gender, p.nickname, p.mobile, p.tel, p.fax, p.email, p.province, p.city, p.address, p.postalcode FROM person p ORDER BY p.uid;postgres=#