Storing JSON in database vs having a new column for each key

Question

I am implementing the following model for storing user related data in my table - I have 2 columns - uid  primary key  and a meta column which stores other data about the user in JSON format      uid     meta --------------------------------------------------  1        name   foo               emailid   foo bar com   bar foo com    --------------------------------------------------  2        name   sann               emailid   sann bar com   sann foo com    --------------------------------------------------   Is this a better way  performance-wise  design-wise  than the one-column-per-property model  where the table will have many columns  like uid  name  emailid    What I like about the first model is  you can add as many fields as possible there is no limitation    Also  I was wondering  now that I have implemented the first model  How do I perform a query on it  like  I want to fetch all the users who have name like  foo    Question - Which is the better way to store user related data  keeping in mind that number of fields is not fixed  in database using - JSON or column-per-field  Also  if the first model is implemented  how to query database as described above  Should I use both the models  by storing all the data which may be searched by a query in a separate row and the other data in JSON  is a different row       Update  Since there won t be too many columns on which I need to perform search  is it wise to use both the models  Key-per-column for the data I need to search and JSON for others  in the same MySQL database

User · Answer

Basically  the first model you are using is called as document-based storage  You should have a look at popular NoSQL document-based database like MongoDB and CouchDB  Basically  in document based db s  you store data in json files and then you can query on these json files   The Second model is the popular relational database structure    If you want to use relational database like MySql then i would suggest you to only use second model  There is no point in using MySql and storing data as in the first model   To answer your second question  there is no way to query name like  foo  if you use first model

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Like most things  it depends    It s not right or wrong good or bad in and of itself to store data in columns or JSON   It depends on what you need to do with it later   What is your predicted way of accessing this data   Will you need to cross reference other data     Other people have answered pretty well what the technical trade-off are   Not many people have discussed that your app and features evolve over time and how this data storage decision impacts your team     Because one of the temptations of using JSON is to avoid migrating schema and so if the team is not disciplined  it s very easy to stick yet another key value pair into a JSON field   There s no migration for it  no one remembers what it s for   There is no validation on it    My team used JSON along side traditional columns in postgres and at first it was the best thing since sliced bread   JSON was attractive and powerful  until one day we realized that flexibility came at a cost and it s suddenly a real pain point   Sometimes that point creeps up really quickly and then it becomes hard to change because we ve built so many other things on top of this design decision   Overtime  adding new features  having the data in JSON led to more complicated looking queries than what might have been added if we stuck to traditional columns   So then we started fishing certain key values back out into columns so that we could make joins and make comparisons between values   Bad idea   Now we had duplication   A new developer would come on board and be confused   Which is the value I should be saving back into   The JSON one or the column   The JSON fields became junk drawers for little pieces of this and that   No data validation on the database level  no consistency or integrity between documents   That pushed all that responsibility into the app instead of getting hard type and constraint checking from traditional columns   Looking back  JSON allowed us to iterate very quickly and get something out the door   It was great   However after we reached a certain team size it s flexibility also allowed us to hang ourselves with a long rope of technical debt which then slowed down subsequent feature evolution progress   Use with caution   Think long and hard about what the nature of your data is   It s the foundation of your app   How will the data be used over time   And how is it likely TO CHANGE

User · Answer

the drawback of the approach is exactly what you mentioned    it makes it VERY slow to find things  since each time you need to perform a text-search on it    value per column instead matches the whole string   Your approach  JSON based data  is fine for data you don t need to search by  and just need to display along with your normal data   Edit  Just to clarify  the above goes for classic relational databases  NoSQL use JSON internally  and are probably a better option if that is the desired behavior

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As others have pointed out queries will be slower  I d suggest to add at least an   ID  column to query by that instead

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some time joins on the table will be an overhead  lets say for OLAP  if i have two tables one is ORDERS  table and other one is ORDER DETAILS  For getting all the order details we have to join two tables this will make the query slower when no of rows in the tables increase lets say in millions or so   left right join is too slower than inner join  I Think if we add JSON string Object in the respective ORDERS entry JOIN will be avoided  add report generation will be faster

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Just tossing it out there  but WordPress has a structure for this kind of stuff  at least WordPress was the first place I observed it  it probably originated elsewhere    It allows limitless keys  and is faster to search than using a JSON blob  but not as fast as some of the NoSQL solutions   uid       meta key        meta val ---------------------------------- 1         name            Frank 1         age             12 2         name            Jeremiah 3         fav food        pizza                     EDIT  For storing history multiple keys  uid     meta id        meta key        meta val ---------------------------------------------------- 1        1             name            Frank 1        2             name            John 1        3             age             12 2        4             name            Jeremiah 3        5             fav food        pizza                     and query via something like this   select meta val from  table  where meta key    name  and uid   1 order by meta id desc

User · Answer

It seems that you re mainly hesitating whether to use a relational model or not   As it stands  your example would fit a relational model reasonably well  but the problem may come of course when you need to make this model evolve   If you only have one  or a few pre-determined  levels of attributes for your main entity  user   you could still use an Entity Attribute Value  EAV  model in a relational database   This also has its pros and cons    If you anticipate that you ll get less structured values that you ll want to search using your application  MySQL might not be the best choice here   If you were using PostgreSQL  you could potentially get the best of both worlds   This really depends on the actual structure of the data here    MySQL isn t necessarily the wrong choice either  and the NoSQL options can be of interest  I m just suggesting alternatives    Indeed  PostgreSQL can build index on  immutable  functions  which MySQL can t as far as I know  and in recent versions  you could use PLV8 on the JSON data directly to build indexes on specific JSON elements of interest  which would improve the speed of your queries when searching for that data   EDIT      Since there won t be too many columns on which I need to perform   search  is it wise to use both the models  Key-per-column for the data   I need to search and JSON for others  in the same MySQL database     Mixing the two models isn t necessarily wrong  assuming the extra space is negligible   but it may cause problems if you don t make sure the two data sets are kept in sync  your application must never change one without also updating the other   A good way to achieve this would be to have a trigger perform the automatic update  by running a stored procedure within the database server whenever an update or insert is made  As far as I m aware  the MySQL stored procedure language probably lack support for any sort of JSON processing  Again PostgreSQL with PLV8 support  and possibly other RDBMS with more flexible stored procedure languages  should be more useful  updating your relational column automatically using a trigger is quite similar to updating an index in the same way

User · Answer

You are trying to fit a non-relational model into a relational database  I think you would be better served using a NoSQL database such as MongoDB  There is no predefined schema which fits in with your requirement of having no limitation to the number of fields  see the typical MongoDB collection example   Check out the MongoDB documentation to get an idea of how you d query your documents  e g   db mycollection find              name   sann

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short answer you have to mix between them   use json for data that you are not going to make relations with them like contact data   address   products variabls

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Updated 4 June 2017  Given that this question answer have gained some popularity  I figured it was worth an update   When this question was originally posted  MySQL had no support for JSON data types and the support in PostgreSQL was in its infancy  Since 5 7  MySQL now supports a JSON data type  in a binary storage format   and PostgreSQL JSONB has matured significantly  Both products provide performant JSON types that can store arbitrary documents  including support for indexing specific keys of the JSON object   However  I still stand by my original statement that your default preference  when using a relational database  should still be column-per-value  Relational databases are still built on the assumption of that the data within them will be fairly well normalized  The query planner has better optimization information when looking at columns than when looking at keys in a JSON document  Foreign keys can be created between columns  but not between keys in JSON documents   Importantly  if the majority of your schema is volatile enough to justify using JSON  you might want to at least consider if a relational database is the right choice   That said  few applications are perfectly relational or document-oriented  Most applications have some mix of both  Here are some examples where I personally have found JSON useful in a relational database    When storing email addresses and phone numbers for a contact  where storing them as values in a JSON array is much easier to manage than multiple separate tables Saving arbitrary key value user preferences  where the value can be boolean  textual  or numeric  and you don t want to have separate columns for different data types  Storing configuration data that has no defined schema  if you re building Zapier  or IFTTT and need to store configuration data for each integration    I m sure there are others as well  but these are just a few quick examples   Original Answer  If you really want to be able to add as many fields as you want with no limitation  other than an arbitrary document size limit   consider a NoSQL solution such as MongoDB   For relational databases  use one column per value  Putting a JSON blob in a column makes it virtually impossible to query  and painfully slow when you actually find a query that works    Relational databases take advantage of data types when indexing  and are intended to be implemented with a normalized structure   As a side note  this isn t to say you should never store JSON in a relational database  If you re adding true metadata  or if your JSON is describing information that does not need to be queried and is only used for display  it may be overkill to create a separate column for all of the data points

[mysql] Storing JSON in database vs. having a new column for each key

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