mysql - grouping but ignore if blank -

-

i'm trying group (or @ least make unique) column m_group_name unless group empty. see doesn't yet have group (and edited placed one) while being able see existing groups.

for example;

id  |  m_group_name ---------------------  1  | red  2  | blue  3  |   4  | red  5  |

which, ideally, result in 1 red, 1 blue, , 2 blanks.

i've tried making blanks null , giving uuid value (after adapting similar found here on stackoverflow), seems make every null same value.

select *, ifnull(m_group_name,uuid()) m_group m group m_group

ideally i'd rather not use null honest

edit: realised 'm_group_name' incorrectly labelled 'group' in example - corrected.

select * m length(group) in (0, null) *length(null) return null. length('') return 0.

am right want see rows don't yet have group?

edit: okay, read carefully. how this:

 select * m length(group) not in (0, null) group group  union  select * m length(group) in (0, null)

Comments

Post a Comment

Popular posts from this blog

Javascript line number mapping -

-
magically formatted comments change reported line number of javascript errors in browsers; this: //@line n "f" n line number , f file name. unfortunately, //@line appears ungoogleable. know there documentation on feature, , browsers support it? (i found references here , here .) from can find available in mozilla based browsers. it using js_setoptions command can turn these options on or off depending on values passed. https://developer.mozilla.org/en/js_setoptions
Read more

c# - Is it possible to remove an existing registration from Autofac container builder? -

-
something along lines: builder.registertype<mytype>().as<itype>(); builder.registertype<mytype2>().as<itype>(); builder.deregistertype<mytype>().as<itype>() var container = builder.build(); var types = container.resolve<ienumerable<itype>>(); assert.istrue(types.count == 1); assert.istrue(types[0].gettype == typeof(mytype2)); scenario: go through bunch of assemblies , go register types want make sure have 1 implementation of given type. need before create container. track on own nice if autofac me bit. this cannot done directly using containerbuilder , unless start on new one. mind you, having first built container should able construct new container filtering away unwanted types , reusing registrations first container. this: ... var container = builder.build(); builder = new containerbuilder(); var components = container.componentregistry.registrations .where(cr => cr.activator.limittype != typ...
Read more

php - Mysql PK and FK char(36) vs int(10) -

-
i have read mysql can handle indexes , searches better if tables keys integers rather char(36) uuid's. is worth converting int(10)? note: use 1 server , have have plans use multiple databases concurrently therefore removing 1 of big reasons using uuid. our tables innodb if makes difference. thanks in advance. usually rdbms can handle integer keys pk more efficient, other datatypes. reason how build index column, yes: long dont require string (or other typed) keys, should use integers. however: char(36) , int(10) far away being equal, because int(10) much smaller, char(36). dont know, if require many different keys, should keep in mind. update, complete last paragraph: int(10) 32-bit, char(36) 36 - ^byte^ (= 288-bit). not mean, int consumes less space, means, char(36) has 4 times more different keys.
Read more