How to store schema-less data efficiently in a relational database?

I'm trying to get a nice balance of searchability and speed. I'm experimenting with different methods.

Option 1:
Serialize the array as JSON/PHP serialized array and store it in a 'meta' column.

id  |  name   | meta  
1       Bob       {"city":"GoTown","birthdate":"1980\/8\/14","cat":"Felix"}
2       Alice     {"city":"Streamville","birthdate":"1986\/6\/6","dog":"Rex"}

Option 2:
Store keys and values together in a stack.

user_id  |    key   |   value   
1         name       Bob
1         city       GoTown
1         birthdate  1980/8/14
1         cat        Felix
2         name       Alice
2         city       Streamville
2         birthdate  1986/6/6
2         dog        Rex

Option 3:
3 tables: entites, keys, values. Store each key name only once.

user_id  |   name   
1         Bob
2         Alice

key_id   |   keyname   
1         city
2         birthdate
3         cat
4         dog

user_id   |   key_id   |   value
1          1            GoTown
1          2            1980/8/14
1          3            Felix
2          1            Streamville
2          2            1986/6/6
2          4            Rex

Are there any pitfalls with using any of these strategies? I'd like to eliminate some of them if they have insurmountable disadvantages.

EDIT: Added some data to represent schema-less data

Some really nasty problems would happen with these tables (idea)

-
Data Redundancy (duplicated data) what you need to keep in synchronisation (and you do you check this because MySQL doesn't have an nice JSON to records function?)

-
You can't force correct values on the database (say goodbye to data integrity and hello to garbage-in garbage-out data) example key birthdate could have value "hello"

And you need some kind of pivot query to fetch the key/values

If you really need dynamic key values (EAV) storage there are some more options:

• Maybe MySQL 5.6 NoSQL using the InnoDB memcached Plugin

• XML -> query with xpath

• RDF

• NoSQL like MongoDB

• MariaDB dynamic columns and MariaDB also supports json.

StackExchange Database Administrators Q#51256, answer score: 4