From 5129a3a8a168e3d2061b139c70654ba8b4e71210 Mon Sep 17 00:00:00 2001 From: zdj21jdz Date: Sun, 20 Oct 2019 23:17:42 -0400 Subject: [PATCH 1/2] Added SQL questions, as well as SQL Icon for top section of README --- README.md | 157 +++++++++++++++++++++++++++++++++++++++++++++++++ images/sql.png | Bin 0 -> 23979 bytes 2 files changed, 157 insertions(+) create mode 100644 images/sql.png diff --git a/README.md b/README.md index 47317c0..c700aab 100644 --- a/README.md +++ b/README.md @@ -38,6 +38,9 @@ OpenShift
OpenShift

Beginner :baby:
Bash
Shell Scripting

Beginner :baby:
Advanced :star: + + sql
SQL

Beginner :baby:
Advanced :star: + @@ -2005,6 +2008,160 @@ A short way of using if/else. An example: [[ $a = 1 ]] && b="yes, equal" || b="nope" +## SQL + + +#### :baby: Beginner + +
+What does SQL stand for?
+ +Structured Query Language +
+ +
+How is SQL Different from NoSQL
+ +The main difference is that SQL databases are structured (data is stored in the form of +tables with rows and columns - like an excel spreadsheet table) while NoSQL is +unstructured, and the data storage can vary depending on how the NoSQL DB is set up, such +as key-value pair, document-oriented, etc. +
+ +
+What does it mean when a database is ACID compliant?
+ +ACID stands for Atomicity, Consistency, Isolation, Durability. In order to be ACID compliant, the database much meet each of the four criteria + +**Atomicity** - When a change occurs to the database, it should either succeed or fail as a whole. + +For example, if you were to update a table, the update should completely execute. If it only partially executes, the +update is considered failed as a whole, and will not go through - the DB will revert back to it's original +state before the update occurred. It should also be mentioned that Atomicity ensures that each +transaction is completed as it's own stand alone "unit" - if any part fails, the whole statement fails. + +**Consistency** - any change made to the database should bring it from one valid state into the next. + +For example, if you make a change to the DB, it shouldn't corrupt it. Consistency is upheld by checks and constraints that +are pre-defined in the DB. For example, if you tried to change a value from a string to an int when the column +should be of datatype string, a consistent DB would not allow this transaction to go through, and the action would +not be executed + +**Isolation** - this ensures that a database will never be seen "mid-update" - as multiple transactions are running at +the same time, it should still leave the DB in the same state as if the transactions were being run sequentially. + +For example, let's say that 20 other people were making changes to the database at the same time. At the +time you executed your query, 15 of the 20 changes had gone through, but 5 were still in progress. You should +only see the 15 changes that had completed - you wouldn't see the database mid-update as the change goes through. + +**Durability** - Once a change is committed, it will remain committed regardless of what happens +(power failure, system crash, etc.). This means that all completed transactions +must be recorded in non-voliatile memory. + +Note that SQL is by nature ACID compliant. Certain NoSQL DB's can be ACID compliant depending on +how they operate, but as a general rule of thumb, NoSQL DB's are not considered ACID compliant +
+ +
+When is it best to use SQL? NoSQL?
+ +SQL - Best used when data integrity is crucial. SQL is typically implemented with many +businesses and areas within the finance field due to it's ACID compliance. + +NoSQL - Great if you need to scale things quickly. NoSQL was designed with web applications +in mind, so it works great if you need to quickly spread the same information around to +multiple servers + +Additionally, since NoSQL does not adhere to the strict table with columns and rows structure +that Relational Databases require, you can store different data types together. +
+ +
+What is a Cartesian Product?
+ +A Cartesian product is when all rows from the first table are joined to all rows in the second +table. This can be done implicitly by not defining a key to join, or explicitly by +calling a CROSS JOIN on two tables, such as below: + +Select * from customers **CROSS JOIN** orders; + +Note that a Cartesian product can also be a bad thing - when performing a join +on two tables in which both do not have unique keys, this could cause the returned information +to be incorrect. +
+ +##### SQL Specific Questions + +For these questions, we will be using the Customers and Orders tables shown below: + +**Customers** + +Customer_ID | Customer_Name | Items_in_cart | Cash_spent_to_Date +------------ | ------------- | ------------- | ------------- +100204 | John Smith | 0 | 20.00 +100205 | Jane Smith | 3 | 40.00 +100206 | Bobby Frank | 1 | 100.20 + +**ORDERS** +Customer_ID | Order_ID | Item | Price | Date_sold +------------ | ------------- | ------------- | ------------- | ------------- +100206 | A123 | Rubber Ducky | 2.20 | 2019-09-18 +100206 | A123 | Bubble Bath | 8.00 | 2019-09-18 +100206 | Q987 | 80-Pack TP | 90.00 | 2019-09-20 +100205 | Z001 | Cat Food - Tuna Fish | 10.00 | 2019-08-05 +100205 | Z001 | Cat Food - Chicken | 10.00 | 2019-08-05 +100205 | Z001 | Cat Food - Beef | 10.00 | 2019-08-05 +100205 | Z001 | Cat Food - Kitty quesadilla | 10.00 | 2019-08-05 +100204 | X202 | Coffee | 20.00 | 2019-04-29 + +
+How would I select all fields from this table?
+ +Select * +From Customers; +
+ +
+How many items are in John's cart?
+ +Select Items_in_cart +From Customers +Where Customer_Name = "John Smith"; +
+ +
+What is the sum of all the cash spent across all customers?
+ +Select SUM(Cash_spent_to_Date) as SUM_CASH +From Customers; +
+ +
+How many people have items in their cart?
+ +Select count(1) as Number_of_People_w_items +From Customers +where Items_in_cart > 0; +
+ +
+How many people have items in their cart?
+ +Select count(1) as Number_of_People_w_items +From Customers +where Items_in_cart > 0; +
+ +
+How would you join the customer table to the order table?
+ +You would join them on the unique key. In this case, the unique key is Customer_ID in +both the Customers table and Orders table +
+ + +#### Advanced + ## Scenarios Scenarios are questions which don't have verbal answer and require you one of the following: diff --git a/images/sql.png b/images/sql.png new file mode 100644 index 0000000000000000000000000000000000000000..45b2826fb9292c28d53f70ba1571203f419becfc GIT binary patch literal 23979 zcmZ^Lc_5VU*ZveGDND+dt+Hi_N?8XjQuacYtPv_(vds{qBxETeTc{)?CRB=H$d+|V z*}@DX`!dET%$S+q{fzp2Ki~I#e}9#k`?=S1pL3n-T+hUwH$A&^``+y^7;LA(IX!b2 zY%}=pX4tl^;Gbp0cPb3#aMM8Vq$T3Vd^YD3(K7=~SwT(%;}4r-_H90SL%P~O5I5JP z#LoG7|A@%>^SpdKyU8c|W47ZF%7qb?h#N8c4#+=$j^^0>+6euuZ|d`>W>wA07ha;x zHIGkK8%w-LeYF2=Owi{c_2ZPP<4r9x#SOoWoM9F|>o7k(eX&9P-1Hcg&S8kM3W@28 z(mSB>MBF@gMOIAt3t2DUI@PcVZ`kC-K~E2H>{iY_a-=@A7Z-4GN&3~I?{~7uF2-z% zc%J0Gq;oIcwJygR_Pu%lcfeww*(;Hr*81g-aST=g(tfqK@YtN3CU-Fib3AaA3eF{8v%_>7-+K&GcZW&yxGmR!SI3;bOCE zYN_R=m&cQ|;&;fQ=@LHNLOt831rwnSKk$B&$=?t)zxGX)JNR;G7``?(_` zBYS@RbgR9TI{WB_B;CWh_vXR;3u~kGksLgZF_kaRA6(aKVIC0z=jJ{We& zsdit=gc?$XqLnd;91oMCrhQ2VEje()_%nvet(oHa9a#dGj`PmL*ky4$-JCDq@S1SH z{v;~9advvz_Uv<1A?Nv%uB=6QAo~uA*_T+k2fq@37h|1u;)ChuP3Zz^qt1ACo<_N` z`1tsa3vP(B&(43yZf1ve!J$DVjL~0rB5+KJmpT3HBAb~8%rECt6+d2E-BnbDXf2J1 z;|t%*&)VffIQ7lG%Db2RMFp52LEGj{>B1|C&d?Z>_g6g|bt`NX#g#^}8ErgJ--~yc z)dtgt`CEIAkkQu=otx74{F*|!kL>?08u76-274D}`(~6oRRU@{(i5kO$Y#{WNfIR- zkH7J`^5vL6kkyP%SQZMJZ|r@}PBXSL#bHL#K$SL#bS>6}lxA z5YWHEe5<+nnHg5xC$8#_Zt)gCT|Ui&BX5Q-)jj+A&fZ?%K{1h$~88pxJ?7*Pn4lY ziA4+Q4-H+$$TE{t@eO}~n2zG8O;qxk5%?e~xk!eLcSgS<0 zBUjovg}my`X2O@9VBTJl}P@nsX%yvWPNUCmq=Iu>A9 zp*dT-Dt}Ve&SdOHsZ5)xk+FX}Lhr}pJd-!8NHXeQU>}^{m>_PLprX_?QX=rCz!ou<9z~G6QV1>;bXd#A$X%U zwsIsNXA$DYPt?`wpAWXWGQ}MEsZl?L3cu<*YS4tOtPCDI_3Vc7e;Ow@<4eZ$cN&l6 z{>%P&tBW7%Gd;}zF3ku@Fh0oeXVXS&z*NTYd>xz`Fp6R$if23P29DHwYMW(NcbKnx z?sfEsxu4Od<_aUWK^F03HEW(rHtUxe>jr}zFQWL&&Ch3hl!f?)12_CH+v^{=x1^_Y z=5Isq@i4fI5AF^ya#^2lr~Xap-u%+%GKNa=`ntO}jt&Y=^3x<@%+s)cTi@I5e1*!` zhkrNi2TnmCZt|?&oP)DUwDKIRW9Ejm2| zeCykWTxk_%Rwt$vORhfCL7kqipsrsKBa|##mhW4UBE(;p{wS~X-$$;7$Z{$<&=vOd&@+n$qY~;m!de(-l1FU ztGx!4X4Np(5x+`Lm_1{G* zWstCnU1~^9Ws$ifa?oOW8%_abZrZ3pT@M|e9ZmtapkyL7@oKw3y|%XYY@tOJv>;`% zoFCuj4RwzwTu*T5>pkNOep8g`gpZn~U&zw$FKbuGGcLdhD}tZ78_Mek$6;Z1EvWNO zU;*)yNc@FEdzeW{Ng7n*;9*rbq8Eb=aa@ZVzd3#U`cpgii?0Wp+5x`ofNvR?lNwlf zU|3v)S{xbJsU)E62(NbIjv#+O0v=1^zq#<`7vXmp=?wsYbLBRbk!r_|y@~Q#+aBms zAV*K80(>Jy`fOE8!-}~!M6SGk_W^ZOWjuBL>(^&d!}7iJBjc1caSBy0?Cbb<;J4cN zX$L6x{j3!5bcy?5QK9m5hiSV0L*Ch<(Op7(f+l2>0(hSLnYx$ z{LRCv7^O+=!scJn*;)}c!2)K9Ho0w+D)PCZplMZxhbU2fl!wUZ-@>_sS<(>_aTKI5 zym~8ncI<$2lr4DSr=~vJgCHx>xbLY>!>nOWEVs~phDwQO#Ef$0S4C&?TOD{pQKBmfvI6+`m|LH~1ZASLBDPR&X6soh8_y z2W+yJ%g)o%Sy%rcSq_N|QLFW9An2RP?siHHk%0g7jh+ znA;_tz9}TQz{1juiaY#$J%ZT1;F(*)b88S1ZhTjbkf%i%I^~7c`DYX?8&afnf5JNM zhb-%=Eb`_Azyiq9LLxbFaAXV5>`LE(d&8Y7m!muR_x<32pG68ri$)AwAnHmka)YK2 z72|B))$6&@>GR>lK zWuqF$maqeJDi4G{Rg7jl#JQ9Be~7@N5u})Ss@i4uxm3`LB$3(J*cr-u8sP`WQ5;`a zQMS$R%;AFfjJLnu8v`dyx_BYD$<2JH5ebWy!T8f)lx@BVJr?IRVCee(Mf;J~*|4W* zw6As}ucIWUDNYb)rCpW!dn;~B&RhDvtU4hNS1&~3qRwrhPo76zMvlBy1Ao=-u^mWL zcG5X5ONWm2w)Mf?Az*~gMayW_EFs>6-&>XQFsNcfGjX0ejX;0Fk7#@n$@2Q;q$Cg9+I%lf8hom}-*K^f zq;=EkVX!nwjKtkjOx-+f<31Gr0obEYv;)x7jvwu*ysV|~j9)0RY^%r_houjH1zy4$ z@oGxM-p#hr~3ISQCl&lVBBzNF@u{TO#dLjzl!<%;;zn)-HCU+?YVy2I)){=RBQ z!EqS4bGBoxMcR9h-0jb}2sZz2K~;s_`7|rgomt`#~BQ(uNI5!@W#Udm`Zc9pya*9M~hpx%8Nuf#xbJ7VGLqC=uCxA+;uG$nGP{! 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What does SQL stand for?
Structured Query Language +
@@ -2103,6 +2104,7 @@ Customer_ID | Customer_Name | Items_in_cart | Cash_spent_to_Date 100206 | Bobby Frank | 1 | 100.20 **ORDERS** + Customer_ID | Order_ID | Item | Price | Date_sold ------------ | ------------- | ------------- | ------------- | ------------- 100206 | A123 | Rubber Ducky | 2.20 | 2019-09-18 @@ -2117,38 +2119,30 @@ Customer_ID | Order_ID | Item | Price | Date_sold
How would I select all fields from this table?
-Select * +Select *
From Customers;
How many items are in John's cart?
-Select Items_in_cart -From Customers +Select Items_in_cart
+From Customers
Where Customer_Name = "John Smith";
What is the sum of all the cash spent across all customers?
-Select SUM(Cash_spent_to_Date) as SUM_CASH +Select SUM(Cash_spent_to_Date) as SUM_CASH
From Customers;
How many people have items in their cart?
-Select count(1) as Number_of_People_w_items -From Customers -where Items_in_cart > 0; -
- -
-How many people have items in their cart?
- -Select count(1) as Number_of_People_w_items -From Customers +Select count(1) as Number_of_People_w_items
+From Customers
where Items_in_cart > 0;
@@ -2159,9 +2153,42 @@ You would join them on the unique key. In this case, the unique key is Customer_ both the Customers table and Orders table
+
+How would you show which customer ordered which items?
+ +Select c.Customer_Name, o.Item
+From Customers c
+Left Join Orders o
+ On c.Customer_ID = o.Customer_ID; + +
+ #### Advanced +
+Using a with statement, how would you show who ordered cat food, and the total amount of money spent?
+ +with cat_food as (
+Select Customer_ID, SUM(Price) as TOTAL_PRICE
+From Orders
+Where Item like "%Cat Food%"
+Group by Customer_ID
+)
+Select Customer_name, TOTAL_PRICE
+From Customers c
+Inner JOIN cat_food f
+ ON c.Customer_ID = f.Customer_ID
+where c.Customer_ID in (Select Customer_ID from cat_food); + +Although this was a simple statement, the "with" clause really shines is when +a complex query needs to be run on a table before joining to another. With statements are nice, +because you create a pseudo temp when running your query, instead of creating a whole new table. + +The Sum of all the purchases of cat food weren't readily available, so we used a with statement to create +the pseudo table to retrieve the sum of the prices spent by each customer, then join the table normally. +
+ ## Scenarios Scenarios are questions which don't have verbal answer and require you one of the following: