小编obj*_*jah的帖子

在postgresql 8.1升级到9.0之后,我发现了库依赖的问题.Postgresql工作正常(连接,查询).

yum list postgresql*
Installed Packages
postgresql.i386 9.0.0-1PGDG.el5 installed
postgresql-debuginfo.i386 9.0.0-1PGDG.el5 installed
postgresql-devel.i386 9.0.0-1PGDG.el5 installed
postgresql-libs.i386 9.0.0-1PGDG.el5 installed
postgresql-odbcng.i386 0.90.101-2.el5 installed
postgresql-plruby.i386 0.5.1-5.el5 installed
postgresql-server.i386 9.0.0-1PGDG.el5 install

但当我试图为红宝石安装'pg'时,我收到了

gem install pg
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
        ERROR: Failed to build gem native extension.

/usr/local/bin/ruby extconf.rb
checking for pg_config... no
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack …

是否有任何选项可以在不使用临时表或过程的情况下获取一个 SQL查询中所有元素的计数组合？

考虑这三个表:

• 产品(id,product_name)

• 交易(身份证明,日期)

• transaction_has_product(id,product_id,transaction_id)

样本数据

• 制品

  1   AAA
  2   BBB
  3   CCC
  

  Run Code Online (Sandbox Code Playgroud)

• 交易

  1   some_date
  2   some_date
  

  Run Code Online (Sandbox Code Playgroud)

• transaction_has_products

  1   1   1
  2   2   1
  3   3   1
  4   1   2
  5   2   2
  

  Run Code Online (Sandbox Code Playgroud)

结果应该是:

AAA, BBB = 2   
AAA, CCC = 1   
BBB, CCC = 1   
AAA, BBB, CCC = 1